Guard more bulk-updates behind lock (#13)

.envrc

@@ -1 +1,23 @@
 use flake
+DOTNET_PATH=$(readlink "$(which dotnet)")
+SETTINGS_FILE=$(find . -maxdepth 1 -type f -name '*.sln.DotSettings.user')
+MSBUILD=$(realpath "$(find "$(dirname "$DOTNET_PATH")/../share/dotnet/sdk" -maxdepth 2 -type f -name MSBuild.dll)")
+if [ -f "$SETTINGS_FILE" ] ; then
+    xmlstarlet ed --inplace \
+    -N wpf="http://schemas.microsoft.com/winfx/2006/xaml/presentation" \
+    -N x="http://schemas.microsoft.com/winfx/2006/xaml" \
+    -N s="clr-namespace:System;assembly=mscorlib" \
+    -N ss="urn:shemas-jetbrains-com:settings-storage-xaml" \
+    --update "//s:String[@x:Key='/Default/Environment/Hierarchy/Build/BuildTool/DotNetCliExePath/@EntryValue']" \
+    --value "$(realpath "$(dirname "$DOTNET_PATH")/../share/dotnet/dotnet")" \
+    "$SETTINGS_FILE"
+
+    xmlstarlet ed --inplace \
+    -N wpf="http://schemas.microsoft.com/winfx/2006/xaml/presentation" \
+    -N x="http://schemas.microsoft.com/winfx/2006/xaml" \
+    -N s="clr-namespace:System;assembly=mscorlib" \
+    -N ss="urn:shemas-jetbrains-com:settings-storage-xaml" \
+    --update "//s:String[@x:Key='/Default/Environment/Hierarchy/Build/BuildTool/CustomBuildToolPath/@EntryValue']" \
+    --value "$MSBUILD" \
+    "$SETTINGS_FILE"
+fi

README.md

@@ -17,7 +17,7 @@ An [expect-testing](https://blog.janestreet.com/the-joy-of-expect-tests/) librar
 
 The basic mechanism works.
 Snapshot updating is vibe-coded with Opus 4 and is purely text-based; I didn't want to use the F# compiler services because that's a pretty heavyweight dependency which should be confined to a separate test runner entity.
-It's not very well tested, and I expect it to be kind of brittle.
+It's fairly well tested, but you will certainly be able to find ways to break it; try not to be too fancy with your syntax around the `snapshot` statement.
 
 # How to use
 
@@ -46,6 +46,58 @@ let ``This test fails: plain text comparison of ToString`` () =
     }
 ```
 
+You can adjust the formatting:
+
+```fsharp
+[<Test>]
+let ``Overriding the formatting`` () =
+    expect {
+        // doesn't matter which order these two lines are in
+        withFormat (fun x -> x.GetType().Name)
+        snapshot @"Int32"
+        return 123
+    }
+```
+
+You can override the JSON serialisation if you find the snapshot format displeasing:
+
+```fsharp
+[<Test>]
+let ``Override JSON serialisation`` () =
+    expect {
+        snapshotJson "<excerpted>"
+
+        withJsonSerializerOptions (
+            let options = JsonFSharpOptions.ThothLike().ToJsonSerializerOptions ()
+            options.WriteIndented <- true
+            options
+        )
+
+        return myComplexAlgebraicDataType
+    }
+```
+
+You can adjust the JSON snapshot parsing if you like, e.g. if you want to add comments to your snapshot text:
+
+```fsharp
+[<Test>]
+let ``Overriding JSON parse`` () =
+    expect {
+        // Without a custom JsonDocumentOptions, WoofWare.Expect would fail to parse this as JSON
+        // and would unconditionally declare that the snapshot did not match:
+        snapshotJson @"{
+            // a key here
+            ""a"":3
+        }"
+
+        // But you can override the JsonDocumentOptions to state that comments are fine:
+        withJsonDocOptions (JsonDocumentOptions (CommentHandling = JsonCommentHandling.Skip))
+        return Map.ofList [ "a", 3 ]
+    }
+```
+
+## Updating an individual snapshot
+
 If a snapshot is failing, add a `'` to the `expect` builder and rerun.
 The rerun will throw, but it will update the snapshot; then remove the `'` again to put the test back into "assert snapshot" mode.
 
@@ -78,6 +130,51 @@ let ``Example of automatically updating`` () =
     }
 ```
 
+## Bulk update of snapshots
+
+*Warning*: when doing this, you should probably make sure your test fixture is `[<Parallelizable(ParallelScope.Children)>]` or less parallelizable,
+or the equivalent in your test runner of choice.
+Otherwise, the global state used by this mechanism may interfere with other fixtures.
+
+You can put WoofWare.Expect into "bulk update" mode as follows:
+
+```fsharp
+open NUnit.Framework
+open WoofWare.Expect
+
+[<TestFixture>]
+[<NonParallelizable>]
+module BulkUpdateExample =
+
+    [<OneTimeSetUp>]
+    let ``Prepare to bulk-update tests`` () =
+        // If you don't want to enter bulk-update mode, just replace this line with a no-op `()`.
+        // The `updateAllSnapshots` tear-down below will simply do nothing in that case.
+        GlobalBuilderConfig.enterBulkUpdateMode ()
+
+    [<OneTimeTearDown>]
+    let ``Update all tests`` () =
+        GlobalBuilderConfig.updateAllSnapshots ()
+
+    [<Test>]
+    let ``Snapshot 2`` () =
+        // this snapshot fails: the "expected" isn't even JSON!
+        expect {
+            snapshotJson ""
+
+            return Map.ofList [ "1", "hi" ; "2", "my" ; "3", "name" ; "4", "is" ]
+        }
+
+    [<Test>]
+    let ``Snapshot 1`` () =
+        // this snapshot fails: the "expected" is not equal to the "actual"
+        expect {
+            snapshotJson @"124"
+            return 123
+        }
+```
+
+Observe the `OneTimeSetUp` which sets global state to enter "bulk update" mode, and the `OneTimeTearDown` which performs all the updates to rectify failures which were accumulated during this test run.
 
 # Limitations
 

WoofWare.Expect.Test/BulkUpdateExample.fs

@@ -0,0 +1,48 @@
+namespace WoofWare.Expect.Test
+
+open WoofWare.Expect
+open NUnit.Framework
+
+[<TestFixture>]
+[<Parallelizable(ParallelScope.Children)>]
+module BulkUpdateExample =
+
+    [<OneTimeSetUp>]
+    let ``Prepare to bulk-update tests`` () =
+        // Uncomment the `enterBulkUpdateMode` to cause all failing tests to accumulate their results
+        // into a global mutable collection.
+        // At the end of the test run, you should then call `updateAllSnapshots ()`
+        // to commit these accumulated failures to the source files.
+        //
+        // When in bulk update mode, all tests will fail, to remind you to exit bulk update mode afterwards.
+        //
+        // We *strongly* recommend making these test fixtures `[<Parallelizable(ParallelScope.Children)>]`
+        // or less parallelisable.
+
+        // GlobalBuilderConfig.enterBulkUpdateMode ()
+        ()
+
+    [<OneTimeTearDown>]
+    let ``Update all tests`` () =
+        GlobalBuilderConfig.updateAllSnapshots ()
+
+    [<Test>]
+    let ``Snapshot 2`` () =
+        expect {
+            snapshotJson
+                @"{
+  ""1"": ""hi"",
+  ""2"": ""my"",
+  ""3"": ""name"",
+  ""4"": ""is""
+}"
+
+            return Map.ofList [ "1", "hi" ; "2", "my" ; "3", "name" ; "4", "is" ]
+        }
+
+    [<Test>]
+    let ``Snapshot 1`` () =
+        expect {
+            snapshotJson @"123"
+            return 123
+        }

WoofWare.Expect.Test/SimpleTest.fs

@@ -1,5 +1,8 @@
 namespace WoofWare.Expect.Test
 
+open System.Collections.Generic
+open System.Text.Json
+open System.Text.Json.Serialization
 open WoofWare.Expect
 open NUnit.Framework
 
@@ -41,3 +44,133 @@ actual was:
             snapshot @"123"
             return 123
         }
+
+    [<Test>]
+    let ``Formatting example`` () =
+        expect {
+            withFormat (fun x -> x.GetType().Name)
+            snapshot @"Int32"
+            return 123
+        }
+
+        expect {
+            snapshot @"Int32"
+            withFormat (fun x -> x.GetType().Name)
+            return 123
+        }
+
+    [<Test>]
+    let ``Custom JSON output`` () =
+        // Out of the box, comments in snapshots cause the JSON parser to throw, so the snapshot fails to match...
+        expect {
+            snapshot
+                @"snapshot mismatch! snapshot at file.fs:99 (Custom JSON output) was:
+
+- [JSON failed to parse:] {
+-     // a key here
+-     ""a"":3
+- }
+
+actual was:
+
++ {
++   ""a"": 3
++ }"
+
+            return
+                Assert.Throws<ExpectException> (fun () ->
+                    expectWithMockedFilePath ("file.fs", 99) {
+                        snapshotJson
+                            @"{
+    // a key here
+    ""a"":3
+}"
+
+                        return Map.ofList [ "a", 3 ]
+                    }
+                )
+                |> _.Message
+        }
+
+        // but it can be made to like them!
+        expect {
+            snapshotJson
+                @"{
+                // a key here
+                ""a"":3
+            }"
+
+            withJsonDocOptions (JsonDocumentOptions (CommentHandling = JsonCommentHandling.Skip))
+            return Map.ofList [ "a", 3 ]
+        }
+
+    type SomeDu =
+        | Something of IReadOnlyDictionary<string, string>
+        | SomethingElse of string
+
+    type MoreComplexType =
+        {
+            Thing : int
+            SomeDu : SomeDu option
+        }
+
+    [<Test>]
+    let ``JSON snapshot of complex ADT`` () =
+        expect {
+            snapshotJson
+                @"{
+  ""SomeDu"": {
+    ""Case"": ""Something"",
+    ""Fields"": [
+      {
+        ""hi"": ""bye""
+      }
+    ]
+  },
+  ""Thing"": 3,
+}"
+
+            return
+                {
+                    Thing = 3
+                    SomeDu = Some (SomeDu.Something (Map.ofList [ "hi", "bye" ]))
+                }
+        }
+
+    [<Test>]
+    let ``Overriding JSON format, from docstring`` () =
+        expect {
+            snapshotJson @"{""a"":3}"
+            withJsonSerializerOptions (JsonSerializerOptions (WriteIndented = false))
+            return Map.ofList [ "a", 3 ]
+        }
+
+    [<Test>]
+    let ``Overriding the JSON format`` () =
+        expect {
+            snapshotJson
+                @"{
+  ""Thing"": 3,
+  ""SomeDu"": [
+    ""Some"",
+    [
+      ""Something"",
+      {
+        ""hi"": ""bye""
+      }
+    ]
+  ]
+}"
+
+            withJsonSerializerOptions (
+                let options = JsonFSharpOptions.ThothLike().ToJsonSerializerOptions ()
+                options.WriteIndented <- true
+                options
+            )
+
+            return
+                {
+                    Thing = 3
+                    SomeDu = Some (SomeDu.Something (Map.ofList [ "hi", "bye" ]))
+                }
+        }

WoofWare.Expect.Test/SyntaxCases/CommentsAndSpacing.fs

@@ -0,0 +1,44 @@
+namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let multipleComments () =
+        expect {
+            snapshot (* first comment *) (* second comment *)
+                (* third comment on new line *)
+                @"test with many comments"
+
+            return 123
+        }
+
+    let nestedComments () =
+        expect {
+            snapshot (* outer (* inner *) comment *) """nested comment test"""
+            return "nested"
+        }
+
+    let commentWithSpecialChars () =
+        expect {
+            snapshot (* comment with "quotes" and \ backslash *) "regular string"
+            return "special"
+        }
+
+    let lotsOfWhitespace () =
+        expect {
+            snapshot
+
+
+                "string after whitespace"
+
+            return "whitespace"
+        }
+
+    let mixedWhitespaceAndComments () =
+        expect {
+            snapshotJson (* comment 1 *)
+                (* comment 2 *)
+                (* comment 3 *) @"123"
+
+            return 123
+        }

WoofWare.Expect.Test/SyntaxCases/EdgeCases.fs

@@ -0,0 +1,69 @@
+namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let emptyString () =
+        expect {
+            snapshot ""
+            return ""
+        }
+
+    let emptyVerbatim () =
+        expect {
+            snapshot @""
+            return ""
+        }
+
+    let emptyTripleQuote () =
+        expect {
+            snapshot """"""
+            return ""
+        }
+
+    let onlyWhitespace () =
+        expect {
+            snapshot "   \t\n   "
+            return "whitespace"
+        }
+
+    let quotesInQuotes () =
+        expect {
+            snapshot @"He said ""Hello"" and she said ""Hi"""
+            return "quotes"
+        }
+
+    let backslashesGalore () =
+        expect {
+            snapshot @"C:\Users\Test\Documents\file.txt"
+            return "path"
+        }
+
+    let veryLongLine () =
+        expect {
+            snapshot
+                @"This is a very long line that goes on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and contains over 300 characters to test how the parser handles very long single-line strings"
+
+            return "long line"
+        }
+
+    let leadingNewlines () =
+        expect {
+            snapshot
+                """
+
+Starts with newlines"""
+
+            return "leading"
+        }
+
+    let trailingNewlines () =
+        expect {
+            snapshot
+                """Ends with newlines
+
+
+"""
+
+            return "trailing"
+        }

WoofWare.Expect.Test/SyntaxCases/MultilineComplex.fs

@@ -0,0 +1,84 @@
+namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let veryLongMultiline () =
+        expect {
+            snapshot
+                """Line 1
+Line 2
+Line 3
+Line 4
+Line 5
+Line 6
+Line 7
+Line 8
+Line 9
+Line 10
+    Indented line 11
+        More indented line 12
+Line 13
+Line 14
+Line 15"""
+
+            return "long"
+        }
+
+    let multilineWithEmptyLines () =
+        expect {
+            snapshot
+                @"First line
+
+Third line
+
+
+Sixth line"
+
+            return "empty lines"
+        }
+
+    let multilineWithSpecialChars () =
+        expect {
+            snapshot
+                """Special chars:
+    Tab:	here
+    Quotes: "double" and 'single'
+    Backslash: \ and \\
+    Unicode: 🎯
+    Regex: .*+?[]"""
+
+            return "special"
+        }
+
+    let multilineJson () =
+        expect {
+            snapshotJson
+                @"{
+  ""name"": ""test"",
+  ""values"": [
+    1,
+    2,
+    3
+  ],
+  ""nested"": {
+    ""deep"": true
+  }
+}"
+
+            return
+                {
+                    name = "test"
+                    values = [ 1 ; 2 ; 3 ]
+                    nested =
+                        {|
+                            deep = true
+                        |}
+                }
+        }
+
+    let windowsLineEndings () =
+        expect {
+            snapshot "Line 1\r\nLine 2\r\nLine 3"
+            return "crlf"
+        }

WoofWare.Expect.Test/SyntaxCases/RegexMetacharacters.fs

@@ -0,0 +1,28 @@
+namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let regexChars () =
+        expect {
+            snapshot @"test with regex chars: .*+?[]{}()|^$\ and more"
+            return 123
+        }
+
+    let regexInTripleQuote () =
+        expect {
+            snapshot """regex: .*+?[]{}()|^$\ in triple quotes"""
+            return 456
+        }
+
+    let regexInRegularString () =
+        expect {
+            snapshot "escaped regex: \\.\\*\\+\\?\\[\\]\\{\\}\\(\\)\\|\\^\\$\\\\"
+            return 789
+        }
+
+    let complexRegexPattern () =
+        expect {
+            snapshotJson @"^(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$"
+            return "IP regex"
+        }

WoofWare.Expect.Test/SyntaxCases/UnicodeCharacters.fs

@@ -0,0 +1,47 @@
+namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let emoji () =
+        expect {
+            snapshot @"Hello 👋 World 🌍 with emoji 🎉🎊"
+            return 123
+        }
+
+    let chineseCharacters () =
+        expect {
+            snapshot """Chinese: 你好世界"""
+            return "hello"
+        }
+
+    let arabicRTL () =
+        expect {
+            snapshot @"Arabic RTL: مرحبا بالعالم"
+            return "rtl test"
+        }
+
+    let combiningCharacters () =
+        expect {
+            // Combining diacritics: e + ́ = é
+            snapshot "test with combining: e\u0301 and a\u0308"
+            return "combining"
+        }
+
+    let mixedScripts () =
+        expect {
+            snapshotJson @"Mixed: English, русский, 日本語, العربية, emoji 🚀"
+            return [ "multilingual" ]
+        }
+
+    let zeroWidthChars () =
+        expect {
+            snapshot @"Zero​width​space​test" // Contains U+200B
+            return "zwsp"
+        }
+
+    let mathSymbols () =
+        expect {
+            snapshot """Math: ∀x∈ℝ, ∃y: x² + y² = 1 ⟹ |x| ≤ 1"""
+            return "math"
+        }

WoofWare.Expect.Test/TestSnapshotFinding/TestCommentsAndSpacing.fs

@@ -0,0 +1,313 @@
+namespace WoofWare.Expect.Test
+
+open WoofWare.Expect
+open NUnit.Framework
+
+[<TestFixture>]
+[<Parallelizable(ParallelScope.Children)>]
+module TestCommentsAndSpacing =
+    [<OneTimeSetUp>]
+    let ``Prepare to bulk-update tests`` () =
+        // GlobalBuilderConfig.enterBulkUpdateMode ()
+        ()
+
+    [<OneTimeTearDown>]
+    let ``Update all tests`` () =
+        GlobalBuilderConfig.updateAllSnapshots ()
+
+    type Dummy = class end
+
+    [<Test>]
+    let ``Multiple comments between snapshot and string`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "CommentsAndSpacing.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let multipleComments () =
+        expect {
+            snapshot (* first comment *) (* second comment *)
+                (* third comment on new line *)
+                @""updated after many comments""
+
+            return 123
+        }
+
+    let nestedComments () =
+        expect {
+            snapshot (* outer (* inner *) comment *) """"""nested comment test""""""
+            return ""nested""
+        }
+
+    let commentWithSpecialChars () =
+        expect {
+            snapshot (* comment with ""quotes"" and \ backslash *) ""regular string""
+            return ""special""
+        }
+
+    let lotsOfWhitespace () =
+        expect {
+            snapshot
+
+
+                ""string after whitespace""
+
+            return ""whitespace""
+        }
+
+    let mixedWhitespaceAndComments () =
+        expect {
+            snapshotJson (* comment 1 *)
+                (* comment 2 *)
+                (* comment 3 *) @""123""
+
+            return 123
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine source 8 "updated after many comments"
+                |> String.concat "\n"
+        }
+
+    [<Test>]
+    let ``Nested comments`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "CommentsAndSpacing.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let multipleComments () =
+        expect {
+            snapshot (* first comment *) (* second comment *)
+                (* third comment on new line *)
+                @""test with many comments""
+
+            return 123
+        }
+
+    let nestedComments () =
+        expect {
+            snapshot (* outer (* inner *) comment *) @""updated after nested comments""
+            return ""nested""
+        }
+
+    let commentWithSpecialChars () =
+        expect {
+            snapshot (* comment with ""quotes"" and \ backslash *) ""regular string""
+            return ""special""
+        }
+
+    let lotsOfWhitespace () =
+        expect {
+            snapshot
+
+
+                ""string after whitespace""
+
+            return ""whitespace""
+        }
+
+    let mixedWhitespaceAndComments () =
+        expect {
+            snapshotJson (* comment 1 *)
+                (* comment 2 *)
+                (* comment 3 *) @""123""
+
+            return 123
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine source 17 "updated after nested comments"
+                |> String.concat "\n"
+        }
+
+    [<Test>]
+    let ``Comment with special chars`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "CommentsAndSpacing.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let multipleComments () =
+        expect {
+            snapshot (* first comment *) (* second comment *)
+                (* third comment on new line *)
+                @""test with many comments""
+
+            return 123
+        }
+
+    let nestedComments () =
+        expect {
+            snapshot (* outer (* inner *) comment *) """"""nested comment test""""""
+            return ""nested""
+        }
+
+    let commentWithSpecialChars () =
+        expect {
+            snapshot (* comment with ""quotes"" and \ backslash *) @""updated after weird comment""
+            return ""special""
+        }
+
+    let lotsOfWhitespace () =
+        expect {
+            snapshot
+
+
+                ""string after whitespace""
+
+            return ""whitespace""
+        }
+
+    let mixedWhitespaceAndComments () =
+        expect {
+            snapshotJson (* comment 1 *)
+                (* comment 2 *)
+                (* comment 3 *) @""123""
+
+            return 123
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine source 23 "updated after weird comment"
+                |> String.concat "\n"
+        }
+
+    [<Test>]
+    let ``Whitespace before`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "CommentsAndSpacing.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let multipleComments () =
+        expect {
+            snapshot (* first comment *) (* second comment *)
+                (* third comment on new line *)
+                @""test with many comments""
+
+            return 123
+        }
+
+    let nestedComments () =
+        expect {
+            snapshot (* outer (* inner *) comment *) """"""nested comment test""""""
+            return ""nested""
+        }
+
+    let commentWithSpecialChars () =
+        expect {
+            snapshot (* comment with ""quotes"" and \ backslash *) ""regular string""
+            return ""special""
+        }
+
+    let lotsOfWhitespace () =
+        expect {
+            snapshot
+
+
+                @""updated after spaces""
+
+            return ""whitespace""
+        }
+
+    let mixedWhitespaceAndComments () =
+        expect {
+            snapshotJson (* comment 1 *)
+                (* comment 2 *)
+                (* comment 3 *) @""123""
+
+            return 123
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine source 29 "updated after spaces"
+                |> String.concat "\n"
+        }
+
+    [<Test>]
+    let ``Mixed whitespace and comments`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "CommentsAndSpacing.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let multipleComments () =
+        expect {
+            snapshot (* first comment *) (* second comment *)
+                (* third comment on new line *)
+                @""test with many comments""
+
+            return 123
+        }
+
+    let nestedComments () =
+        expect {
+            snapshot (* outer (* inner *) comment *) """"""nested comment test""""""
+            return ""nested""
+        }
+
+    let commentWithSpecialChars () =
+        expect {
+            snapshot (* comment with ""quotes"" and \ backslash *) ""regular string""
+            return ""special""
+        }
+
+    let lotsOfWhitespace () =
+        expect {
+            snapshot
+
+
+                ""string after whitespace""
+
+            return ""whitespace""
+        }
+
+    let mixedWhitespaceAndComments () =
+        expect {
+            snapshotJson (* comment 1 *)
+                (* comment 2 *)
+                (* comment 3 *) @""updated after comments""
+
+            return 123
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine source 39 "updated after comments"
+                |> String.concat "\n"
+        }

WoofWare.Expect.Test/TestSnapshotFinding/TestEdgeCases.fs

@@ -0,0 +1,781 @@
+namespace WoofWare.Expect.Test
+
+open NUnit.Framework
+open WoofWare.Expect
+
+[<TestFixture>]
+module TestEdgeCases =
+    [<OneTimeSetUp>]
+    let ``Prepare to bulk-update tests`` () =
+        // GlobalBuilderConfig.enterBulkUpdateMode ()
+        ()
+
+    [<OneTimeTearDown>]
+    let ``Update all tests`` () =
+        GlobalBuilderConfig.updateAllSnapshots ()
+
+    type Dummy = class end
+
+    [<Test>]
+    let ``Empty string replacements`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "EdgeCases.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let emptyString () =
+        expect {
+            snapshot @""now has content""
+            return """"
+        }
+
+    let emptyVerbatim () =
+        expect {
+            snapshot @""""
+            return """"
+        }
+
+    let emptyTripleQuote () =
+        expect {
+            snapshot """"""""""""
+            return """"
+        }
+
+    let onlyWhitespace () =
+        expect {
+            snapshot ""   \t\n   ""
+            return ""whitespace""
+        }
+
+    let quotesInQuotes () =
+        expect {
+            snapshot @""He said """"Hello"""" and she said """"Hi""""""
+            return ""quotes""
+        }
+
+    let backslashesGalore () =
+        expect {
+            snapshot @""C:\Users\Test\Documents\file.txt""
+            return ""path""
+        }
+
+    let veryLongLine () =
+        expect {
+            snapshot
+                @""This is a very long line that goes on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and contains over 300 characters to test how the parser handles very long single-line strings""
+
+            return ""long line""
+        }
+
+    let leadingNewlines () =
+        expect {
+            snapshot
+                """"""
+
+Starts with newlines""""""
+
+            return ""leading""
+        }
+
+    let trailingNewlines () =
+        expect {
+            snapshot
+                """"""Ends with newlines
+
+
+""""""
+
+            return ""trailing""
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine source 8 "now has content"
+                |> String.concat "\n"
+        }
+
+    [<Test>]
+    let ``Empty string replacements, verbatim`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "EdgeCases.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let emptyString () =
+        expect {
+            snapshot """"
+            return """"
+        }
+
+    let emptyVerbatim () =
+        expect {
+            snapshot @""now has content""
+            return """"
+        }
+
+    let emptyTripleQuote () =
+        expect {
+            snapshot """"""""""""
+            return """"
+        }
+
+    let onlyWhitespace () =
+        expect {
+            snapshot ""   \t\n   ""
+            return ""whitespace""
+        }
+
+    let quotesInQuotes () =
+        expect {
+            snapshot @""He said """"Hello"""" and she said """"Hi""""""
+            return ""quotes""
+        }
+
+    let backslashesGalore () =
+        expect {
+            snapshot @""C:\Users\Test\Documents\file.txt""
+            return ""path""
+        }
+
+    let veryLongLine () =
+        expect {
+            snapshot
+                @""This is a very long line that goes on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and contains over 300 characters to test how the parser handles very long single-line strings""
+
+            return ""long line""
+        }
+
+    let leadingNewlines () =
+        expect {
+            snapshot
+                """"""
+
+Starts with newlines""""""
+
+            return ""leading""
+        }
+
+    let trailingNewlines () =
+        expect {
+            snapshot
+                """"""Ends with newlines
+
+
+""""""
+
+            return ""trailing""
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine source 14 "now has content"
+                |> String.concat "\n"
+        }
+
+    [<Test>]
+    let ``Empty string replacements, triple quotes`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "EdgeCases.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let emptyString () =
+        expect {
+            snapshot """"
+            return """"
+        }
+
+    let emptyVerbatim () =
+        expect {
+            snapshot @""""
+            return """"
+        }
+
+    let emptyTripleQuote () =
+        expect {
+            snapshot @""now has content""
+            return """"
+        }
+
+    let onlyWhitespace () =
+        expect {
+            snapshot ""   \t\n   ""
+            return ""whitespace""
+        }
+
+    let quotesInQuotes () =
+        expect {
+            snapshot @""He said """"Hello"""" and she said """"Hi""""""
+            return ""quotes""
+        }
+
+    let backslashesGalore () =
+        expect {
+            snapshot @""C:\Users\Test\Documents\file.txt""
+            return ""path""
+        }
+
+    let veryLongLine () =
+        expect {
+            snapshot
+                @""This is a very long line that goes on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and contains over 300 characters to test how the parser handles very long single-line strings""
+
+            return ""long line""
+        }
+
+    let leadingNewlines () =
+        expect {
+            snapshot
+                """"""
+
+Starts with newlines""""""
+
+            return ""leading""
+        }
+
+    let trailingNewlines () =
+        expect {
+            snapshot
+                """"""Ends with newlines
+
+
+""""""
+
+            return ""trailing""
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine source 20 "now has content"
+                |> String.concat "\n"
+        }
+
+    [<Test>]
+    let ``Empty string replacements, only whitespace`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "EdgeCases.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let emptyString () =
+        expect {
+            snapshot """"
+            return """"
+        }
+
+    let emptyVerbatim () =
+        expect {
+            snapshot @""""
+            return """"
+        }
+
+    let emptyTripleQuote () =
+        expect {
+            snapshot """"""""""""
+            return """"
+        }
+
+    let onlyWhitespace () =
+        expect {
+            snapshot @""now has content""
+            return ""whitespace""
+        }
+
+    let quotesInQuotes () =
+        expect {
+            snapshot @""He said """"Hello"""" and she said """"Hi""""""
+            return ""quotes""
+        }
+
+    let backslashesGalore () =
+        expect {
+            snapshot @""C:\Users\Test\Documents\file.txt""
+            return ""path""
+        }
+
+    let veryLongLine () =
+        expect {
+            snapshot
+                @""This is a very long line that goes on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and contains over 300 characters to test how the parser handles very long single-line strings""
+
+            return ""long line""
+        }
+
+    let leadingNewlines () =
+        expect {
+            snapshot
+                """"""
+
+Starts with newlines""""""
+
+            return ""leading""
+        }
+
+    let trailingNewlines () =
+        expect {
+            snapshot
+                """"""Ends with newlines
+
+
+""""""
+
+            return ""trailing""
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine source 26 "now has content"
+                |> String.concat "\n"
+        }
+
+    [<Test>]
+    let ``Quotes in quotes handling`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "EdgeCases.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let emptyString () =
+        expect {
+            snapshot """"
+            return """"
+        }
+
+    let emptyVerbatim () =
+        expect {
+            snapshot @""""
+            return """"
+        }
+
+    let emptyTripleQuote () =
+        expect {
+            snapshot """"""""""""
+            return """"
+        }
+
+    let onlyWhitespace () =
+        expect {
+            snapshot ""   \t\n   ""
+            return ""whitespace""
+        }
+
+    let quotesInQuotes () =
+        expect {
+            snapshot @""Updated: He said """"What's up?"""" and replied """"Nothing much.""""""
+            return ""quotes""
+        }
+
+    let backslashesGalore () =
+        expect {
+            snapshot @""C:\Users\Test\Documents\file.txt""
+            return ""path""
+        }
+
+    let veryLongLine () =
+        expect {
+            snapshot
+                @""This is a very long line that goes on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and contains over 300 characters to test how the parser handles very long single-line strings""
+
+            return ""long line""
+        }
+
+    let leadingNewlines () =
+        expect {
+            snapshot
+                """"""
+
+Starts with newlines""""""
+
+            return ""leading""
+        }
+
+    let trailingNewlines () =
+        expect {
+            snapshot
+                """"""Ends with newlines
+
+
+""""""
+
+            return ""trailing""
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine
+                    source
+                    32
+                    "Updated: He said \"What's up?\" and replied \"Nothing much.\""
+                |> String.concat "\n"
+        }
+
+    [<Test>]
+    let ``Backslashes galore`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "EdgeCases.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let emptyString () =
+        expect {
+            snapshot """"
+            return """"
+        }
+
+    let emptyVerbatim () =
+        expect {
+            snapshot @""""
+            return """"
+        }
+
+    let emptyTripleQuote () =
+        expect {
+            snapshot """"""""""""
+            return """"
+        }
+
+    let onlyWhitespace () =
+        expect {
+            snapshot ""   \t\n   ""
+            return ""whitespace""
+        }
+
+    let quotesInQuotes () =
+        expect {
+            snapshot @""He said """"Hello"""" and she said """"Hi""""""
+            return ""quotes""
+        }
+
+    let backslashesGalore () =
+        expect {
+            snapshot @""prefer\these\ones""
+            return ""path""
+        }
+
+    let veryLongLine () =
+        expect {
+            snapshot
+                @""This is a very long line that goes on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and contains over 300 characters to test how the parser handles very long single-line strings""
+
+            return ""long line""
+        }
+
+    let leadingNewlines () =
+        expect {
+            snapshot
+                """"""
+
+Starts with newlines""""""
+
+            return ""leading""
+        }
+
+    let trailingNewlines () =
+        expect {
+            snapshot
+                """"""Ends with newlines
+
+
+""""""
+
+            return ""trailing""
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine source 38 "prefer\\these\\ones"
+                |> String.concat "\n"
+        }
+
+    [<Test>]
+    let ``Very long line`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "EdgeCases.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let emptyString () =
+        expect {
+            snapshot """"
+            return """"
+        }
+
+    let emptyVerbatim () =
+        expect {
+            snapshot @""""
+            return """"
+        }
+
+    let emptyTripleQuote () =
+        expect {
+            snapshot """"""""""""
+            return """"
+        }
+
+    let onlyWhitespace () =
+        expect {
+            snapshot ""   \t\n   ""
+            return ""whitespace""
+        }
+
+    let quotesInQuotes () =
+        expect {
+            snapshot @""He said """"Hello"""" and she said """"Hi""""""
+            return ""quotes""
+        }
+
+    let backslashesGalore () =
+        expect {
+            snapshot @""C:\Users\Test\Documents\file.txt""
+            return ""path""
+        }
+
+    let veryLongLine () =
+        expect {
+            snapshot
+                @""this line is short though""
+
+            return ""long line""
+        }
+
+    let leadingNewlines () =
+        expect {
+            snapshot
+                """"""
+
+Starts with newlines""""""
+
+            return ""leading""
+        }
+
+    let trailingNewlines () =
+        expect {
+            snapshot
+                """"""Ends with newlines
+
+
+""""""
+
+            return ""trailing""
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine source 44 "this line is short though"
+                |> String.concat "\n"
+        }
+
+    [<Test>]
+    let ``Leading newlines`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "EdgeCases.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let emptyString () =
+        expect {
+            snapshot """"
+            return """"
+        }
+
+    let emptyVerbatim () =
+        expect {
+            snapshot @""""
+            return """"
+        }
+
+    let emptyTripleQuote () =
+        expect {
+            snapshot """"""""""""
+            return """"
+        }
+
+    let onlyWhitespace () =
+        expect {
+            snapshot ""   \t\n   ""
+            return ""whitespace""
+        }
+
+    let quotesInQuotes () =
+        expect {
+            snapshot @""He said """"Hello"""" and she said """"Hi""""""
+            return ""quotes""
+        }
+
+    let backslashesGalore () =
+        expect {
+            snapshot @""C:\Users\Test\Documents\file.txt""
+            return ""path""
+        }
+
+    let veryLongLine () =
+        expect {
+            snapshot
+                @""This is a very long line that goes on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and contains over 300 characters to test how the parser handles very long single-line strings""
+
+            return ""long line""
+        }
+
+    let leadingNewlines () =
+        expect {
+            snapshot
+                @""
+
+Just newlines!
+
+
+""
+
+            return ""leading""
+        }
+
+    let trailingNewlines () =
+        expect {
+            snapshot
+                """"""Ends with newlines
+
+
+""""""
+
+            return ""trailing""
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine source 52 "\n\nJust newlines!\n\n\n"
+                |> String.concat "\n"
+        }
+
+    [<Test>]
+    let ``Trailing newlines`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "EdgeCases.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let emptyString () =
+        expect {
+            snapshot """"
+            return """"
+        }
+
+    let emptyVerbatim () =
+        expect {
+            snapshot @""""
+            return """"
+        }
+
+    let emptyTripleQuote () =
+        expect {
+            snapshot """"""""""""
+            return """"
+        }
+
+    let onlyWhitespace () =
+        expect {
+            snapshot ""   \t\n   ""
+            return ""whitespace""
+        }
+
+    let quotesInQuotes () =
+        expect {
+            snapshot @""He said """"Hello"""" and she said """"Hi""""""
+            return ""quotes""
+        }
+
+    let backslashesGalore () =
+        expect {
+            snapshot @""C:\Users\Test\Documents\file.txt""
+            return ""path""
+        }
+
+    let veryLongLine () =
+        expect {
+            snapshot
+                @""This is a very long line that goes on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and contains over 300 characters to test how the parser handles very long single-line strings""
+
+            return ""long line""
+        }
+
+    let leadingNewlines () =
+        expect {
+            snapshot
+                """"""
+
+Starts with newlines""""""
+
+            return ""leading""
+        }
+
+    let trailingNewlines () =
+        expect {
+            snapshot
+                @""
+
+Just newlines!
+
+
+""
+
+            return ""trailing""
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine source 62 "\n\nJust newlines!\n\n\n"
+                |> String.concat "\n"
+        }

WoofWare.Expect.Test/TestSnapshotFinding/TestMultilineComplex.fs

@@ -0,0 +1,483 @@
+namespace WoofWare.Expect.Test
+
+open NUnit.Framework
+open WoofWare.Expect
+
+[<TestFixture>]
+module TestMultilineComplex =
+    [<OneTimeSetUp>]
+    let ``Prepare to bulk-update tests`` () =
+        // GlobalBuilderConfig.enterBulkUpdateMode ()
+        ()
+
+    [<OneTimeTearDown>]
+    let ``Update all tests`` () =
+        GlobalBuilderConfig.updateAllSnapshots ()
+
+    type Dummy = class end
+
+    [<Test>]
+    let ``Very long multiline string`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "MultilineComplex.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let veryLongMultiline () =
+        expect {
+            snapshot
+                @""Replaced with
+a different
+multiline
+value""
+
+            return ""long""
+        }
+
+    let multilineWithEmptyLines () =
+        expect {
+            snapshot
+                @""First line
+
+Third line
+
+
+Sixth line""
+
+            return ""empty lines""
+        }
+
+    let multilineWithSpecialChars () =
+        expect {
+            snapshot
+                """"""Special chars:
+    Tab:	here
+    Quotes: ""double"" and 'single'
+    Backslash: \ and \\
+    Unicode: 🎯
+    Regex: .*+?[]""""""
+
+            return ""special""
+        }
+
+    let multilineJson () =
+        expect {
+            snapshotJson
+                @""{
+  """"name"""": """"test"""",
+  """"values"""": [
+    1,
+    2,
+    3
+  ],
+  """"nested"""": {
+    """"deep"""": true
+  }
+}""
+
+            return
+                {
+                    name = ""test""
+                    values = [ 1 ; 2 ; 3 ]
+                    nested =
+                        {|
+                            deep = true
+                        |}
+                }
+        }
+
+    let windowsLineEndings () =
+        expect {
+            snapshot ""Line 1\r\nLine 2\r\nLine 3""
+            return ""crlf""
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine source 8 "Replaced with\na different\nmultiline\nvalue"
+                |> String.concat "\n"
+        }
+
+    [<Test>]
+    let ``Multiline with empty lines`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "MultilineComplex.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let veryLongMultiline () =
+        expect {
+            snapshot
+                """"""Line 1
+Line 2
+Line 3
+Line 4
+Line 5
+Line 6
+Line 7
+Line 8
+Line 9
+Line 10
+    Indented line 11
+        More indented line 12
+Line 13
+Line 14
+Line 15""""""
+
+            return ""long""
+        }
+
+    let multilineWithEmptyLines () =
+        expect {
+            snapshot
+                @""Replaced with
+
+a different
+multiline
+value""
+
+            return ""empty lines""
+        }
+
+    let multilineWithSpecialChars () =
+        expect {
+            snapshot
+                """"""Special chars:
+    Tab:	here
+    Quotes: ""double"" and 'single'
+    Backslash: \ and \\
+    Unicode: 🎯
+    Regex: .*+?[]""""""
+
+            return ""special""
+        }
+
+    let multilineJson () =
+        expect {
+            snapshotJson
+                @""{
+  """"name"""": """"test"""",
+  """"values"""": [
+    1,
+    2,
+    3
+  ],
+  """"nested"""": {
+    """"deep"""": true
+  }
+}""
+
+            return
+                {
+                    name = ""test""
+                    values = [ 1 ; 2 ; 3 ]
+                    nested =
+                        {|
+                            deep = true
+                        |}
+                }
+        }
+
+    let windowsLineEndings () =
+        expect {
+            snapshot ""Line 1\r\nLine 2\r\nLine 3""
+            return ""crlf""
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine source 30 "Replaced with\n\na different\nmultiline\nvalue"
+                |> String.concat "\n"
+        }
+
+    [<Test>]
+    let ``Multiline with special chars`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "MultilineComplex.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let veryLongMultiline () =
+        expect {
+            snapshot
+                """"""Line 1
+Line 2
+Line 3
+Line 4
+Line 5
+Line 6
+Line 7
+Line 8
+Line 9
+Line 10
+    Indented line 11
+        More indented line 12
+Line 13
+Line 14
+Line 15""""""
+
+            return ""long""
+        }
+
+    let multilineWithEmptyLines () =
+        expect {
+            snapshot
+                @""First line
+
+Third line
+
+
+Sixth line""
+
+            return ""empty lines""
+        }
+
+    let multilineWithSpecialChars () =
+        expect {
+            snapshot
+                @""get rid of it all""
+
+            return ""special""
+        }
+
+    let multilineJson () =
+        expect {
+            snapshotJson
+                @""{
+  """"name"""": """"test"""",
+  """"values"""": [
+    1,
+    2,
+    3
+  ],
+  """"nested"""": {
+    """"deep"""": true
+  }
+}""
+
+            return
+                {
+                    name = ""test""
+                    values = [ 1 ; 2 ; 3 ]
+                    nested =
+                        {|
+                            deep = true
+                        |}
+                }
+        }
+
+    let windowsLineEndings () =
+        expect {
+            snapshot ""Line 1\r\nLine 2\r\nLine 3""
+            return ""crlf""
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine source 43 "get rid of it all"
+                |> String.concat "\n"
+        }
+
+    [<Test>]
+    let ``Complex nested JSON with Unicode`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "MultilineComplex.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let veryLongMultiline () =
+        expect {
+            snapshot
+                """"""Line 1
+Line 2
+Line 3
+Line 4
+Line 5
+Line 6
+Line 7
+Line 8
+Line 9
+Line 10
+    Indented line 11
+        More indented line 12
+Line 13
+Line 14
+Line 15""""""
+
+            return ""long""
+        }
+
+    let multilineWithEmptyLines () =
+        expect {
+            snapshot
+                @""First line
+
+Third line
+
+
+Sixth line""
+
+            return ""empty lines""
+        }
+
+    let multilineWithSpecialChars () =
+        expect {
+            snapshot
+                """"""Special chars:
+    Tab:	here
+    Quotes: ""double"" and 'single'
+    Backslash: \ and \\
+    Unicode: 🎯
+    Regex: .*+?[]""""""
+
+            return ""special""
+        }
+
+    let multilineJson () =
+        expect {
+            snapshotJson
+                @""wheeeee""
+
+            return
+                {
+                    name = ""test""
+                    values = [ 1 ; 2 ; 3 ]
+                    nested =
+                        {|
+                            deep = true
+                        |}
+                }
+        }
+
+    let windowsLineEndings () =
+        expect {
+            snapshot ""Line 1\r\nLine 2\r\nLine 3""
+            return ""crlf""
+        }
+"
+
+            return SnapshotUpdate.updateSnapshotAtLine source 56 "wheeeee" |> String.concat "\n"
+        }
+
+    [<Test>]
+    let ``Windows line endings`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "MultilineComplex.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let veryLongMultiline () =
+        expect {
+            snapshot
+                """"""Line 1
+Line 2
+Line 3
+Line 4
+Line 5
+Line 6
+Line 7
+Line 8
+Line 9
+Line 10
+    Indented line 11
+        More indented line 12
+Line 13
+Line 14
+Line 15""""""
+
+            return ""long""
+        }
+
+    let multilineWithEmptyLines () =
+        expect {
+            snapshot
+                @""First line
+
+Third line
+
+
+Sixth line""
+
+            return ""empty lines""
+        }
+
+    let multilineWithSpecialChars () =
+        expect {
+            snapshot
+                """"""Special chars:
+    Tab:	here
+    Quotes: ""double"" and 'single'
+    Backslash: \ and \\
+    Unicode: 🎯
+    Regex: .*+?[]""""""
+
+            return ""special""
+        }
+
+    let multilineJson () =
+        expect {
+            snapshotJson
+                @""{
+  """"name"""": """"test"""",
+  """"values"""": [
+    1,
+    2,
+    3
+  ],
+  """"nested"""": {
+    """"deep"""": true
+  }
+}""
+
+            return
+                {
+                    name = ""test""
+                    values = [ 1 ; 2 ; 3 ]
+                    nested =
+                        {|
+                            deep = true
+                        |}
+                }
+        }
+
+    let windowsLineEndings () =
+        expect {
+            snapshot @""down with line endings""
+            return ""crlf""
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine source 82 "down with line endings"
+                |> String.concat "\n"
+        }

WoofWare.Expect.Test/TestSnapshotFinding/TestRegexMetacharacters.fs

@@ -0,0 +1,190 @@
+namespace WoofWare.Expect.Test
+
+open WoofWare.Expect
+open NUnit.Framework
+
+[<TestFixture>]
+[<Parallelizable(ParallelScope.Children)>]
+module TestRegexMetacharacters =
+    [<OneTimeSetUp>]
+    let ``Prepare to bulk-update tests`` () =
+        // GlobalBuilderConfig.enterBulkUpdateMode ()
+        ()
+
+    [<OneTimeTearDown>]
+    let ``Update all tests`` () =
+        GlobalBuilderConfig.updateAllSnapshots ()
+
+    type Dummy = class end
+
+    [<Test>]
+    let ``Regex metacharacters in verbatim string`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "RegexMetacharacters.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let regexChars () =
+        expect {
+            snapshot @""replacement with .*+?[]{}()|^$\ chars""
+            return 123
+        }
+
+    let regexInTripleQuote () =
+        expect {
+            snapshot """"""regex: .*+?[]{}()|^$\ in triple quotes""""""
+            return 456
+        }
+
+    let regexInRegularString () =
+        expect {
+            snapshot ""escaped regex: \\.\\*\\+\\?\\[\\]\\{\\}\\(\\)\\|\\^\\$\\\\""
+            return 789
+        }
+
+    let complexRegexPattern () =
+        expect {
+            snapshotJson @""^(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$""
+            return ""IP regex""
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine source 8 "replacement with .*+?[]{}()|^$\\ chars"
+                |> String.concat "\n"
+        }
+
+    [<Test>]
+    let ``Regex metacharacters in triple quote`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "RegexMetacharacters.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let regexChars () =
+        expect {
+            snapshot @""test with regex chars: .*+?[]{}()|^$\ and more""
+            return 123
+        }
+
+    let regexInTripleQuote () =
+        expect {
+            snapshot @""new regex: [a-z]+(?:\d{2,4})? pattern""
+            return 456
+        }
+
+    let regexInRegularString () =
+        expect {
+            snapshot ""escaped regex: \\.\\*\\+\\?\\[\\]\\{\\}\\(\\)\\|\\^\\$\\\\""
+            return 789
+        }
+
+    let complexRegexPattern () =
+        expect {
+            snapshotJson @""^(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$""
+            return ""IP regex""
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine source 14 "new regex: [a-z]+(?:\\d{2,4})? pattern"
+                |> String.concat "\n"
+        }
+
+    [<Test>]
+    let ``Regex metacharacters in regular string`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "RegexMetacharacters.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let regexChars () =
+        expect {
+            snapshot @""test with regex chars: .*+?[]{}()|^$\ and more""
+            return 123
+        }
+
+    let regexInTripleQuote () =
+        expect {
+            snapshot """"""regex: .*+?[]{}()|^$\ in triple quotes""""""
+            return 456
+        }
+
+    let regexInRegularString () =
+        expect {
+            snapshot @""new regex: [a-z]+(?:\d{2,4})? pattern""
+            return 789
+        }
+
+    let complexRegexPattern () =
+        expect {
+            snapshotJson @""^(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$""
+            return ""IP regex""
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine source 20 "new regex: [a-z]+(?:\\d{2,4})? pattern"
+                |> String.concat "\n"
+        }
+
+    [<Test>]
+    let ``IP regex`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "RegexMetacharacters.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let regexChars () =
+        expect {
+            snapshot @""test with regex chars: .*+?[]{}()|^$\ and more""
+            return 123
+        }
+
+    let regexInTripleQuote () =
+        expect {
+            snapshot """"""regex: .*+?[]{}()|^$\ in triple quotes""""""
+            return 456
+        }
+
+    let regexInRegularString () =
+        expect {
+            snapshot ""escaped regex: \\.\\*\\+\\?\\[\\]\\{\\}\\(\\)\\|\\^\\$\\\\""
+            return 789
+        }
+
+    let complexRegexPattern () =
+        expect {
+            snapshotJson @""new regex: [a-z]+(?:\d{2,4})? pattern""
+            return ""IP regex""
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine source 26 "new regex: [a-z]+(?:\\d{2,4})? pattern"
+                |> String.concat "\n"
+        }

WoofWare.Expect.Test/TestSnapshotFinding/TestSnapshotFinding.fs

@@ -4,7 +4,16 @@ open WoofWare.Expect
 open NUnit.Framework
 
 [<TestFixture>]
+[<Parallelizable(ParallelScope.Children)>]
 module TestSnapshotFinding =
+    [<OneTimeSetUp>]
+    let ``Prepare to bulk-update tests`` () =
+        // GlobalBuilderConfig.enterBulkUpdateMode ()
+        ()
+
+    [<OneTimeTearDown>]
+    let ``Update all tests`` () =
+        GlobalBuilderConfig.updateAllSnapshots ()
 
     type Dummy = class end
 

WoofWare.Expect.Test/TestSnapshotFinding/TestUnicodeCharacters.fs

@@ -0,0 +1,456 @@
+namespace WoofWare.Expect.Test
+
+open NUnit.Framework
+open WoofWare.Expect
+
+[<TestFixture>]
+module TestUnicodeCharacters =
+    [<OneTimeSetUp>]
+    let ``Prepare to bulk-update tests`` () =
+        // GlobalBuilderConfig.enterBulkUpdateMode ()
+        ()
+
+    [<OneTimeTearDown>]
+    let ``Update all tests`` () =
+        GlobalBuilderConfig.updateAllSnapshots ()
+
+    type Dummy = class end
+
+    [<Test>]
+    let ``Unicode emoji in string`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "UnicodeCharacters.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let emoji () =
+        expect {
+            snapshot @""Updated with 🚀🌟✨ more emoji!""
+            return 123
+        }
+
+    let chineseCharacters () =
+        expect {
+            snapshot """"""Chinese: 你好世界""""""
+            return ""hello""
+        }
+
+    let arabicRTL () =
+        expect {
+            snapshot @""Arabic RTL: مرحبا بالعالم""
+            return ""rtl test""
+        }
+
+    let combiningCharacters () =
+        expect {
+            // Combining diacritics: e + ́ = é
+            snapshot ""test with combining: e\u0301 and a\u0308""
+            return ""combining""
+        }
+
+    let mixedScripts () =
+        expect {
+            snapshotJson @""Mixed: English, русский, 日本語, العربية, emoji 🚀""
+            return [ ""multilingual"" ]
+        }
+
+    let zeroWidthChars () =
+        expect {
+            snapshot @""Zero​width​space​test"" // Contains U+200B
+            return ""zwsp""
+        }
+
+    let mathSymbols () =
+        expect {
+            snapshot """"""Math: ∀x∈ℝ, ∃y: x² + y² = 1 ⟹ |x| ≤ 1""""""
+            return ""math""
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine source 8 "Updated with 🚀🌟✨ more emoji!"
+                |> String.concat "\n"
+        }
+
+    [<Test>]
+    let ``Unicode Chinese characters multi-line`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "UnicodeCharacters.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let emoji () =
+        expect {
+            snapshot @""Hello 👋 World 🌍 with emoji 🎉🎊""
+            return 123
+        }
+
+    let chineseCharacters () =
+        expect {
+            snapshot @""Chinese poem:
+静夜思
+床前明月光
+疑是地上霜
+举头望明月
+低头思故乡""
+            return ""hello""
+        }
+
+    let arabicRTL () =
+        expect {
+            snapshot @""Arabic RTL: مرحبا بالعالم""
+            return ""rtl test""
+        }
+
+    let combiningCharacters () =
+        expect {
+            // Combining diacritics: e + ́ = é
+            snapshot ""test with combining: e\u0301 and a\u0308""
+            return ""combining""
+        }
+
+    let mixedScripts () =
+        expect {
+            snapshotJson @""Mixed: English, русский, 日本語, العربية, emoji 🚀""
+            return [ ""multilingual"" ]
+        }
+
+    let zeroWidthChars () =
+        expect {
+            snapshot @""Zero​width​space​test"" // Contains U+200B
+            return ""zwsp""
+        }
+
+    let mathSymbols () =
+        expect {
+            snapshot """"""Math: ∀x∈ℝ, ∃y: x² + y² = 1 ⟹ |x| ≤ 1""""""
+            return ""math""
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine source 14 "Chinese poem:\n静夜思\n床前明月光\n疑是地上霜\n举头望明月\n低头思故乡"
+                |> String.concat "\n"
+        }
+
+    [<Test>]
+    let ``Arabic RTL`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "UnicodeCharacters.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let emoji () =
+        expect {
+            snapshot @""Hello 👋 World 🌍 with emoji 🎉🎊""
+            return 123
+        }
+
+    let chineseCharacters () =
+        expect {
+            snapshot """"""Chinese: 你好世界""""""
+            return ""hello""
+        }
+
+    let arabicRTL () =
+        expect {
+            snapshot @""Updated Arabic: مرحبا بالعالم""
+            return ""rtl test""
+        }
+
+    let combiningCharacters () =
+        expect {
+            // Combining diacritics: e + ́ = é
+            snapshot ""test with combining: e\u0301 and a\u0308""
+            return ""combining""
+        }
+
+    let mixedScripts () =
+        expect {
+            snapshotJson @""Mixed: English, русский, 日本語, العربية, emoji 🚀""
+            return [ ""multilingual"" ]
+        }
+
+    let zeroWidthChars () =
+        expect {
+            snapshot @""Zero​width​space​test"" // Contains U+200B
+            return ""zwsp""
+        }
+
+    let mathSymbols () =
+        expect {
+            snapshot """"""Math: ∀x∈ℝ, ∃y: x² + y² = 1 ⟹ |x| ≤ 1""""""
+            return ""math""
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine source 20 "Updated Arabic: مرحبا بالعالم"
+                |> String.concat "\n"
+        }
+
+    [<Test>]
+    let ``Combining characters`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "UnicodeCharacters.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let emoji () =
+        expect {
+            snapshot @""Hello 👋 World 🌍 with emoji 🎉🎊""
+            return 123
+        }
+
+    let chineseCharacters () =
+        expect {
+            snapshot """"""Chinese: 你好世界""""""
+            return ""hello""
+        }
+
+    let arabicRTL () =
+        expect {
+            snapshot @""Arabic RTL: مرحبا بالعالم""
+            return ""rtl test""
+        }
+
+    let combiningCharacters () =
+        expect {
+            // Combining diacritics: e + ́ = é
+            snapshot @""updated test with combining: é and ä!""
+            return ""combining""
+        }
+
+    let mixedScripts () =
+        expect {
+            snapshotJson @""Mixed: English, русский, 日本語, العربية, emoji 🚀""
+            return [ ""multilingual"" ]
+        }
+
+    let zeroWidthChars () =
+        expect {
+            snapshot @""Zero​width​space​test"" // Contains U+200B
+            return ""zwsp""
+        }
+
+    let mathSymbols () =
+        expect {
+            snapshot """"""Math: ∀x∈ℝ, ∃y: x² + y² = 1 ⟹ |x| ≤ 1""""""
+            return ""math""
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine source 27 "updated test with combining: e\u0301 and a\u0308!"
+                |> String.concat "\n"
+        }
+
+    [<Test>]
+    let ``Mixed scripts`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "UnicodeCharacters.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let emoji () =
+        expect {
+            snapshot @""Hello 👋 World 🌍 with emoji 🎉🎊""
+            return 123
+        }
+
+    let chineseCharacters () =
+        expect {
+            snapshot """"""Chinese: 你好世界""""""
+            return ""hello""
+        }
+
+    let arabicRTL () =
+        expect {
+            snapshot @""Arabic RTL: مرحبا بالعالم""
+            return ""rtl test""
+        }
+
+    let combiningCharacters () =
+        expect {
+            // Combining diacritics: e + ́ = é
+            snapshot ""test with combining: e\u0301 and a\u0308""
+            return ""combining""
+        }
+
+    let mixedScripts () =
+        expect {
+            snapshotJson @""Updated mixed: English, русский, 日本語, العربية, emoji 🚀""
+            return [ ""multilingual"" ]
+        }
+
+    let zeroWidthChars () =
+        expect {
+            snapshot @""Zero​width​space​test"" // Contains U+200B
+            return ""zwsp""
+        }
+
+    let mathSymbols () =
+        expect {
+            snapshot """"""Math: ∀x∈ℝ, ∃y: x² + y² = 1 ⟹ |x| ≤ 1""""""
+            return ""math""
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine source 33 "Updated mixed: English, русский, 日本語, العربية, emoji 🚀"
+                |> String.concat "\n"
+        }
+
+    [<Test>]
+    let ``ZWBS character`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "UnicodeCharacters.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let emoji () =
+        expect {
+            snapshot @""Hello 👋 World 🌍 with emoji 🎉🎊""
+            return 123
+        }
+
+    let chineseCharacters () =
+        expect {
+            snapshot """"""Chinese: 你好世界""""""
+            return ""hello""
+        }
+
+    let arabicRTL () =
+        expect {
+            snapshot @""Arabic RTL: مرحبا بالعالم""
+            return ""rtl test""
+        }
+
+    let combiningCharacters () =
+        expect {
+            // Combining diacritics: e + ́ = é
+            snapshot ""test with combining: e\u0301 and a\u0308""
+            return ""combining""
+        }
+
+    let mixedScripts () =
+        expect {
+            snapshotJson @""Mixed: English, русский, 日本語, العربية, emoji 🚀""
+            return [ ""multilingual"" ]
+        }
+
+    let zeroWidthChars () =
+        expect {
+            snapshot @""Updated: Zero​width​space​test"" // Contains U+200B
+            return ""zwsp""
+        }
+
+    let mathSymbols () =
+        expect {
+            snapshot """"""Math: ∀x∈ℝ, ∃y: x² + y² = 1 ⟹ |x| ≤ 1""""""
+            return ""math""
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine source 39 "Updated: Zero​width​space​test"
+                |> String.concat "\n"
+        }
+
+    [<Test>]
+    let ``Maths`` () =
+        let source =
+            Assembly.getEmbeddedResource typeof<Dummy>.Assembly "UnicodeCharacters.fs"
+            |> _.Split('\n')
+
+        expect {
+            snapshot
+                @"namespace BigExample
+
+open WoofWare.Expect
+
+module MyModule =
+    let emoji () =
+        expect {
+            snapshot @""Hello 👋 World 🌍 with emoji 🎉🎊""
+            return 123
+        }
+
+    let chineseCharacters () =
+        expect {
+            snapshot """"""Chinese: 你好世界""""""
+            return ""hello""
+        }
+
+    let arabicRTL () =
+        expect {
+            snapshot @""Arabic RTL: مرحبا بالعالم""
+            return ""rtl test""
+        }
+
+    let combiningCharacters () =
+        expect {
+            // Combining diacritics: e + ́ = é
+            snapshot ""test with combining: e\u0301 and a\u0308""
+            return ""combining""
+        }
+
+    let mixedScripts () =
+        expect {
+            snapshotJson @""Mixed: English, русский, 日本語, العربية, emoji 🚀""
+            return [ ""multilingual"" ]
+        }
+
+    let zeroWidthChars () =
+        expect {
+            snapshot @""Zero​width​space​test"" // Contains U+200B
+            return ""zwsp""
+        }
+
+    let mathSymbols () =
+        expect {
+            snapshot @""Pretty vacuous, huh: ∀x∈ℝ, ∃y: x² + y² = 1 ⟹ |x| ≤ 1""
+            return ""math""
+        }
+"
+
+            return
+                SnapshotUpdate.updateSnapshotAtLine source 45 "Pretty vacuous, huh: ∀x∈ℝ, ∃y: x² + y² = 1 ⟹ |x| ≤ 1"
+                |> String.concat "\n"
+        }

WoofWare.Expect.Test/WoofWare.Expect.Test.fsproj

@@ -1,20 +1,35 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
-        <TargetFramework>net9.0</TargetFramework>
-        <LangVersion>latest</LangVersion>
-        <IsPackable>false</IsPackable>
+      <TargetFramework>net9.0</TargetFramework>
+      <LangVersion>latest</LangVersion>
+      <IsPackable>false</IsPackable>
+      <EnableNUnitRunner>true</EnableNUnitRunner>
+      <OutputType>Exe</OutputType>
+      <TestingPlatformDotnetTestSupport>true</TestingPlatformDotnetTestSupport>
     </PropertyGroup>
 
     <ItemGroup>
       <Compile Include="Assembly.fs" />
+      <Compile Include="BulkUpdateExample.fs" />
       <Compile Include="SimpleTest.fs" />
-      <Compile Include="TestSnapshotFinding.fs" />
       <Compile Include="TestSurface.fs" />
+      <Compile Include="TestSnapshotFinding\TestSnapshotFinding.fs" />
+      <Compile Include="TestSnapshotFinding\TestUnicodeCharacters.fs" />
+      <Compile Include="TestSnapshotFinding\TestMultilineComplex.fs" />
+      <Compile Include="TestSnapshotFinding\TestEdgeCases.fs" />
+      <Compile Include="TestSnapshotFinding\TestCommentsAndSpacing.fs" />
+      <Compile Include="TestSnapshotFinding\TestRegexMetacharacters.fs" />
+
       <EmbeddedResource Include="SyntaxCases\AtStringOneLine.fs" />
       <EmbeddedResource Include="SyntaxCases\SingleQuoteManyLine.fs" />
       <EmbeddedResource Include="SyntaxCases\TripleQuoteInterveningComment.fs" />
       <EmbeddedResource Include="SyntaxCases\TripleQuoteOneLine.fs" />
+      <EmbeddedResource Include="SyntaxCases\RegexMetacharacters.fs" />
+      <EmbeddedResource Include="SyntaxCases\UnicodeCharacters.fs" />
+      <EmbeddedResource Include="SyntaxCases\MultilineComplex.fs" />
+      <EmbeddedResource Include="SyntaxCases\EdgeCases.fs" />
+      <EmbeddedResource Include="SyntaxCases\CommentsAndSpacing.fs" />
     </ItemGroup>
 
     <ItemGroup>

WoofWare.Expect/Builder.fs

@@ -3,39 +3,10 @@
 open System.IO
 open System.Runtime.CompilerServices
 open System.Text.Json
-open System.Text.Json.Serialization
-
-type private CallerInfo =
-    {
-        MemberName : string
-        FilePath : string
-        LineNumber : int
-    }
-
-type private SnapshotValue =
-    | BareString of string
-    | Json of string
 
 /// An exception indicating that a value failed to match its snapshot.
 exception ExpectException of Message : string
 
-/// A dummy type which is here to provide better error messages when you supply
-/// the `snapshot` keyword multiple times.
-type YouHaveSuppliedMultipleSnapshots = private | NonConstructible
-
-/// The state accumulated by the `expect` builder. You should never find yourself interacting with this type.
-type ExpectState<'T> =
-    private
-        {
-            Snapshot : (SnapshotValue * CallerInfo) option
-            Actual : 'T option
-        }
-
-[<RequireQualifiedAccess>]
-module private Text =
-    let predent (c : char) (s : string) =
-        s.Split '\n' |> Seq.map (sprintf "%c %s" c) |> String.concat "\n"
-
 /// <summary>Specify how the Expect computation expression treats failures.</summary>
 /// <remarks>You probably don't want to use this directly; use the computation expression definitions
 /// like <c>expect</c> in the <c>Builder</c> module instead.</remarks>
@@ -64,10 +35,7 @@ type ExpectBuilder (mode : Mode) =
             ExpectBuilder Mode.Assert
 
     /// Combine two `ExpectState`s. The first one is the "expected" snapshot; the second is the "actual".
-    member _.Bind
-        (state : ExpectState<YouHaveSuppliedMultipleSnapshots>, f : unit -> ExpectState<'U>)
-        : ExpectState<'U>
-        =
+    member _.Bind<'U> (state : ExpectState<'U>, f : unit -> ExpectState<'U>) : ExpectState<'U> =
         let actual = f ()
 
         match state.Actual with
@@ -78,23 +46,44 @@ type ExpectBuilder (mode : Mode) =
         | Some _ -> failwith "somehow Actual came through with a Snapshot"
         | None ->
 
+        let formatter =
+            match state.Formatter, actual.Formatter with
+            | None, f -> f
+            | Some f, None -> Some f
+            | Some _, Some _ -> failwith "multiple formatters supplied for a single expect!"
+
+        let jsonSerOptions =
+            match state.JsonSerialiserOptions, actual.JsonSerialiserOptions with
+            | None, f -> f
+            | Some f, None -> Some f
+            | Some _, Some _ -> failwith "multiple JSON serialiser options supplied for a single expect!"
+
+        let jsonDocOptions =
+            match state.JsonDocOptions, actual.JsonDocOptions with
+            | None, f -> f
+            | Some f, None -> Some f
+            | Some _, Some _ -> failwith "multiple JSON document options supplied for a single expect!"
+
         // Pass through the state structure when there's no actual value
         {
+            Formatter = formatter
             Snapshot = state.Snapshot
             Actual = actual.Actual
+            JsonSerialiserOptions = jsonSerOptions
+            JsonDocOptions = jsonDocOptions
         }
 
     /// <summary>Express that the actual value's <c>ToString</c> should identically equal this string.</summary>
     [<CustomOperation("snapshot", MaintainsVariableSpaceUsingBind = true)>]
-    member _.Snapshot
+    member _.Snapshot<'a>
         (
-            state : ExpectState<unit>,
+            state : ExpectState<'a>,
             snapshot : string,
             [<CallerMemberName>] ?memberName : string,
             [<CallerLineNumber>] ?callerLine : int,
             [<CallerFilePath>] ?filePath : string
         )
-        : ExpectState<YouHaveSuppliedMultipleSnapshots>
+        : ExpectState<'a>
         =
         match state.Snapshot with
         | Some _ -> failwith "snapshot can only be specified once"
@@ -110,8 +99,8 @@ type ExpectBuilder (mode : Mode) =
                     LineNumber = lineNumber
                 }
 
-            {
-                Snapshot = Some (SnapshotValue.BareString snapshot, callerInfo)
+            { state with
+                Snapshot = Some (SnapshotValue.Formatted snapshot, callerInfo)
                 Actual = None
             }
 
@@ -120,10 +109,10 @@ type ExpectBuilder (mode : Mode) =
     /// which matches the JSON document that is this string.
     /// </summary>
     /// <remarks>
-    /// For example, <c>snapshot "123"</c> indicates the JSON integer 123.
+    /// For example, <c>snapshotJson "123"</c> indicates the JSON integer 123.
     /// </remarks>
     [<CustomOperation("snapshotJson", MaintainsVariableSpaceUsingBind = true)>]
-    member _.SnapshotJson
+    member _.SnapshotJson<'a>
         (
             state : ExpectState<unit>,
             snapshot : string,
@@ -131,7 +120,7 @@ type ExpectBuilder (mode : Mode) =
             [<CallerLineNumber>] ?callerLine : int,
             [<CallerFilePath>] ?filePath : string
         )
-        : ExpectState<YouHaveSuppliedMultipleSnapshots>
+        : ExpectState<'a>
         =
         match state.Snapshot with
         | Some _ -> failwith "snapshot can only be specified once"
@@ -148,13 +137,89 @@ type ExpectBuilder (mode : Mode) =
                 }
 
             {
+                Formatter = None
+                JsonSerialiserOptions = state.JsonSerialiserOptions
+                JsonDocOptions = state.JsonDocOptions
                 Snapshot = Some (SnapshotValue.Json snapshot, callerInfo)
                 Actual = None
             }
 
+    /// <summary>
+    /// Express that the <c>return</c> value of this builder should be formatted using this function, before
+    /// comparing to the snapshot.
+    /// this value.
+    /// </summary>
+    /// <remarks>
+    /// For example, <c>withFormat (fun x -> x.ToString ()) "123"</c> is equivalent to <c>snapshot "123"</c>.
+    /// </remarks>
+    [<CustomOperation("withFormat", MaintainsVariableSpaceUsingBind = true)>]
+    member _.WithFormat<'T> (state : ExpectState<'T>, formatter : 'T -> string) =
+        match state.Formatter with
+        | Some _ -> failwith "Please don't supply withFormat more than once"
+        | None ->
+            { state with
+                Formatter = Some formatter
+            }
+
+    /// <summary>
+    /// Express that these JsonSerializerOptions should be used to construct the JSON object to which the snapshot
+    /// is to be compared (or, in write-out-the-snapshot mode, to construct the JSON object to be written out).
+    /// </summary>
+    /// <example>
+    /// If you want your snapshots to be written out compactly, rather than the default indenting:
+    /// <code>
+    /// expect {
+    ///     snapshotJson @"{""a"":3}"
+    ///     withJsonSerializerOptions (JsonSerializerOptions (WriteIndented = false))
+    ///     return Map.ofList ["a", 3]
+    /// }
+    /// </code>
+    /// </example>
+    [<CustomOperation("withJsonSerializerOptions", MaintainsVariableSpaceUsingBind = true)>]
+    member _.WithJsonSerializerOptions<'T> (state : ExpectState<'T>, jsonOptions : JsonSerializerOptions) =
+        match state.JsonSerialiserOptions with
+        | Some _ -> failwith "Please don't supply withJsonSerializerOptions more than once"
+        | None ->
+            { state with
+                JsonSerialiserOptions = Some jsonOptions
+            }
+
+    /// <summary>
+    /// Express that these JsonDocumentOptions should be used when parsing the snapshot string into a JSON object.
+    /// </summary>
+    /// <remarks>
+    /// For example, you might use this if you want your snapshot to contain comments;
+    /// the default JSON document parser will instead throw on comments, causing the snapshot instantly to fail to match.
+    /// </remarks>
+    /// <example>
+    /// <code>
+    /// expect {
+    ///     snapshotJson
+    ///         @"{
+    ///         // a key here
+    ///         ""a"":3
+    ///     }"
+    ///
+    ///     withJsonDocOptions (JsonDocumentOptions (CommentHandling = JsonCommentHandling.Skip))
+    ///     return Map.ofList [ "a", 3 ]
+    /// }
+    /// </code>
+    /// </example>
+    [<CustomOperation("withJsonDocOptions", MaintainsVariableSpaceUsingBind = true)>]
+    member _.WithJsonDocOptions<'T> (state : ExpectState<'T>, jsonOptions : JsonDocumentOptions) =
+        match state.JsonDocOptions with
+        | Some _ -> failwith "Please don't supply withJsonDocOptions more than once"
+        | None ->
+            { state with
+                JsonDocOptions = Some jsonOptions
+            }
+
     /// MaintainsVariableSpaceUsingBind causes this to be used; it's a dummy representing "no snapshot and no assertion".
     member _.Return (() : unit) : ExpectState<'T> =
         {
+            Formatter = None
+            JsonSerialiserOptions = None
+            JsonDocOptions = None
             Snapshot = None
             Actual = None
         }
@@ -163,6 +228,9 @@ type ExpectBuilder (mode : Mode) =
     member _.Return (value : 'T) : ExpectState<'T> =
         {
             Snapshot = None
+            Formatter = None
+            JsonDocOptions = None
+            JsonSerialiserOptions = None
             Actual = Some value
         }
 
@@ -171,71 +239,49 @@ type ExpectBuilder (mode : Mode) =
 
     /// Computation expression `Run`, which runs a `Delay`ed snapshot assertion, throwing if the assertion fails.
     member _.Run (f : unit -> ExpectState<'T>) : unit =
-        let state = f ()
+        let state = f () |> CompletedSnapshotGeneric.make
 
-        let options = JsonFSharpOptions.Default().ToJsonSerializerOptions ()
-
-        match state.Snapshot, state.Actual with
-        | Some (snapshot, source), Some actual ->
-            let raiseError (snapshot : string) (actual : string) : unit =
-                match mode with
-                | Mode.AssertMockingSource (mockSource, line) ->
+        let raiseError (snapshot : string) (actual : string) : unit =
+            match mode with
+            | Mode.AssertMockingSource (mockSource, line) ->
+                sprintf
+                    "snapshot mismatch! snapshot at %s:%i (%s) was:\n\n%s\n\nactual was:\n\n%s"
+                    mockSource
+                    line
+                    state.Caller.MemberName
+                    (snapshot |> Text.predent '-')
+                    (actual |> Text.predent '+')
+                |> ExpectException
+                |> raise
+            | Mode.Assert ->
+                if GlobalBuilderConfig.isBulkUpdateMode () then
+                    GlobalBuilderConfig.registerTest state
+                else
                     sprintf
                         "snapshot mismatch! snapshot at %s:%i (%s) was:\n\n%s\n\nactual was:\n\n%s"
-                        mockSource
-                        line
-                        source.MemberName
+                        state.Caller.FilePath
+                        state.Caller.LineNumber
+                        state.Caller.MemberName
                         (snapshot |> Text.predent '-')
                         (actual |> Text.predent '+')
                     |> ExpectException
                     |> raise
-                | Mode.Assert ->
-                    sprintf
-                        "snapshot mismatch! snapshot at %s:%i (%s) was:\n\n%s\n\nactual was:\n\n%s"
-                        source.FilePath
-                        source.LineNumber
-                        source.MemberName
-                        (snapshot |> Text.predent '-')
-                        (actual |> Text.predent '+')
-                    |> ExpectException
-                    |> raise
-                | Mode.Update ->
-                    let lines = File.ReadAllLines source.FilePath
-                    let oldContents = String.concat "\n" lines
-                    let lines = SnapshotUpdate.updateSnapshotAtLine lines source.LineNumber actual
-                    File.WriteAllLines (source.FilePath, lines)
-                    failwith ("Snapshot successfully updated. Previous contents:\n" + oldContents)
+            | Mode.Update ->
+                let lines = File.ReadAllLines state.Caller.FilePath
+                let oldContents = String.concat "\n" lines
+                let lines = SnapshotUpdate.updateSnapshotAtLine lines state.Caller.LineNumber actual
+                File.writeAllLines lines state.Caller.FilePath
+                failwith ("Snapshot successfully updated. Previous contents:\n" + oldContents)
 
-            match snapshot with
-            | SnapshotValue.Json snapshot ->
-                let canonicalSnapshot = JsonDocument.Parse snapshot
-
-                let canonicalActual =
-                    JsonSerializer.Serialize (actual, options) |> JsonDocument.Parse
-
-                if not (JsonElement.DeepEquals (canonicalActual.RootElement, canonicalSnapshot.RootElement)) then
-                    raiseError (canonicalSnapshot.RootElement.ToString ()) (canonicalActual.RootElement.ToString ())
-                else
-                    match mode with
-                    | Mode.Update ->
-                        failwith
-                            "Snapshot assertion passed, but we are in snapshot-updating mode. Use the `expect` builder instead of `expect'` to assert the contents of a snapshot."
-                    | _ -> ()
-
-            | SnapshotValue.BareString snapshot ->
-                let actual = actual.ToString ()
-
-                if actual <> snapshot then
-                    raiseError snapshot actual
-                else
-                    match mode with
-                    | Mode.Update ->
-                        failwith
-                            "Snapshot assertion passed, but we are in snapshot-updating mode. Use the `expect` builder instead of `expect'` to assert the contents of a snapshot."
-                    | _ -> ()
-
-        | None, _ -> failwith "Must specify snapshot"
-        | _, None -> failwith "Must specify actual value with 'return'"
+        match CompletedSnapshotGeneric.passesAssertion state with
+        | None ->
+            match mode, GlobalBuilderConfig.isBulkUpdateMode () with
+            | Mode.Update, _
+            | _, true ->
+                failwith
+                    "Snapshot assertion passed, but we are in snapshot-updating mode. Use the `expect` builder instead of `expect'` to assert the contents of a single snapshot; disable `GlobalBuilderConfig.bulkUpdate` to move back to assertion-checking mode."
+            | _ -> ()
+        | Some (expected, actual) -> raiseError expected actual
 
 /// Module containing the `expect` builder.
 [<AutoOpen>]

WoofWare.Expect/Config.fs

@@ -0,0 +1,71 @@
+namespace WoofWare.Expect
+
+/// Module holding global mutable state controlling the behaviour of WoofWare.Expect
+/// when running in bulk-update mode.
+[<RequireQualifiedAccess>]
+module GlobalBuilderConfig =
+    /// All access to the global mutable state locks on this.
+    let private locker = obj ()
+
+    // Global mutable state ensuring there is at most one `enterBulkUpdateMode`/`updateAllSnapshots` pair running at once.
+    let private bulkUpdate = ref 0
+
+    let private allTests : ResizeArray<CompletedSnapshot> = ResizeArray ()
+
+    let internal isBulkUpdateMode () : bool =
+        lock locker (fun () -> bulkUpdate.Value > 0)
+
+    /// <summary>
+    /// Call this to make the <c>expect</c> builder register all tests for bulk update as it runs.
+    /// </summary>
+    /// <remarks>
+    /// We *strongly* recommend making test fixtures <c>Parallelizable(ParallelScope.Children)</c> or less parallelizable (for NUnit) if you're running in bulk update mode.
+    /// The implied global mutable state is liable to interfere with other expect builders in other fixtures otherwise.
+    /// </remarks>
+    let enterBulkUpdateMode () =
+        lock
+            locker
+            (fun () ->
+                if bulkUpdate.Value <> 0 then
+                    failwith
+                        "WoofWare.Expect requires bulk updates to happen serially: for example, make the test fixture `[<NonParallelizable>]` if you're using NUnit."
+
+                bulkUpdate.Value <- bulkUpdate.Value + 1
+            )
+
+    /// <summary>
+    /// Clear the set of failing tests registered by any previous bulk-update runs.
+    /// </summary>
+    ///
+    /// <remarks>
+    /// You probably don't need to do this, because your test runner is probably tearing down
+    /// anyway after the tests have failed; this is mainly here for WoofWare.Expect's own internal testing.
+    /// </remarks>
+    let clearTests () = lock locker allTests.Clear
+
+    let internal registerTest (s : CompletedSnapshotGeneric<'T>) : unit =
+        let toAdd = s |> CompletedSnapshot.make
+        lock locker (fun () -> allTests.Add toAdd)
+
+    /// <summary>
+    /// For all tests whose failures have already been registered,
+    /// transform the files on disk so that the failing snapshots now pass.
+    /// </summary>
+    let updateAllSnapshots () =
+        // It's OK for this to be called when `enterBulkUpdateMode` has not been called, i.e. when `bulkUpdate` has
+        // value 0. That just means we aren't in bulk-update mode, so we expect the following simply to do nothing.
+        // (This is an expected workflow: we expect users to run `updateAllSnapshots` unconditionally in a
+        // one-time tear-down of the test suite, and they use the one-time setup to control whether any work is actually
+        // performed here.)
+        lock
+            locker
+            (fun () ->
+                let allTests = Seq.toArray allTests
+
+                try
+                    SnapshotUpdate.updateAll allTests
+                finally
+                    // double acquiring of reentrant lock is OK, we're not switching threads
+                    clearTests ()
+                    bulkUpdate.Value <- 0
+            )

WoofWare.Expect/Domain.fs

@@ -0,0 +1,131 @@
+namespace WoofWare.Expect
+
+open System.Text.Json
+open System.Text.Json.Serialization
+
+/// <summary>
+/// Information about where in source code a specific snapshot is located.
+/// </summary>
+type CallerInfo =
+    internal
+        {
+            MemberName : string
+            FilePath : string
+            LineNumber : int
+        }
+
+type private SnapshotValue =
+    | Json of expected : string
+    | Formatted of expected : string
+
+type private CompletedSnapshotValue<'T> =
+    | Json of expected : string * JsonSerializerOptions * JsonDocumentOptions
+    | Formatted of expected : string * format : ('T -> string)
+
+/// The state accumulated by the `expect` builder. You should never find yourself interacting with this type.
+type ExpectState<'T> =
+    private
+        {
+            Formatter : ('T -> string) option
+            JsonSerialiserOptions : JsonSerializerOptions option
+            JsonDocOptions : JsonDocumentOptions option
+            Snapshot : (SnapshotValue * CallerInfo) option
+            Actual : 'T option
+        }
+
+/// The state accumulated by the `expect` builder. You should never find yourself interacting with this type.
+type internal CompletedSnapshotGeneric<'T> =
+    private
+        {
+            SnapshotValue : CompletedSnapshotValue<'T>
+            Caller : CallerInfo
+            Actual : 'T
+        }
+
+[<RequireQualifiedAccess>]
+module internal CompletedSnapshotGeneric =
+    let private defaultJsonSerialiserOptions : JsonSerializerOptions =
+        let options = JsonFSharpOptions.Default().ToJsonSerializerOptions ()
+        options.AllowTrailingCommas <- true
+        options.WriteIndented <- true
+        options
+
+    let private defaultJsonDocOptions : JsonDocumentOptions =
+        let options = JsonDocumentOptions (AllowTrailingCommas = true)
+        options
+
+    let make (state : ExpectState<'T>) : CompletedSnapshotGeneric<'T> =
+        match state.Snapshot, state.Actual with
+        | Some (snapshot, source), Some actual ->
+            let snapshot =
+                match snapshot with
+                | SnapshotValue.Json expected ->
+                    let serOpts =
+                        state.JsonSerialiserOptions |> Option.defaultValue defaultJsonSerialiserOptions
+
+                    let docOpts = state.JsonDocOptions |> Option.defaultValue defaultJsonDocOptions
+                    CompletedSnapshotValue.Json (expected, serOpts, docOpts)
+                | SnapshotValue.Formatted expected ->
+                    let formatter =
+                        match state.Formatter with
+                        | None -> fun x -> x.ToString ()
+                        | Some f -> f
+
+                    CompletedSnapshotValue.Formatted (expected, formatter)
+
+            {
+                SnapshotValue = snapshot
+                Caller = source
+                Actual = actual
+            }
+        | None, _ -> failwith "Must specify snapshot"
+        | _, None -> failwith "Must specify actual value with 'return'"
+
+    let internal replacement (s : CompletedSnapshotGeneric<'T>) =
+        match s.SnapshotValue with
+        | CompletedSnapshotValue.Json (_existing, options, _) ->
+            JsonSerializer.Serialize (s.Actual, options)
+            |> JsonDocument.Parse
+            |> _.RootElement
+            |> _.ToString()
+        | CompletedSnapshotValue.Formatted (_existing, f) -> f s.Actual
+
+    /// Returns None if the assertion passes, or Some (expected, actual) if the assertion fails.
+    let internal passesAssertion (state : CompletedSnapshotGeneric<'T>) : (string * string) option =
+        match state.SnapshotValue with
+        | CompletedSnapshotValue.Formatted (snapshot, f) ->
+            let actual = f state.Actual
+            if actual = snapshot then None else Some (snapshot, actual)
+        | CompletedSnapshotValue.Json (snapshot, jsonSerOptions, jsonDocOptions) ->
+            let canonicalSnapshot =
+                try
+                    JsonDocument.Parse (snapshot, jsonDocOptions) |> Some
+                with _ ->
+                    None
+
+            let canonicalActual =
+                JsonSerializer.Serialize (state.Actual, jsonSerOptions) |> JsonDocument.Parse
+
+            match canonicalSnapshot with
+            | None -> Some ("[JSON failed to parse:] " + snapshot, canonicalActual.RootElement.ToString ())
+            | Some canonicalSnapshot ->
+                if not (JsonElement.DeepEquals (canonicalActual.RootElement, canonicalSnapshot.RootElement)) then
+                    Some (canonicalSnapshot.RootElement.ToString (), canonicalActual.RootElement.ToString ())
+                else
+                    None
+
+/// Represents a snapshot test that has failed and is awaiting update or report to the user.
+type CompletedSnapshot =
+    internal
+        {
+            CallerInfo : CallerInfo
+            Replacement : string
+        }
+
+[<RequireQualifiedAccess>]
+module internal CompletedSnapshot =
+    let make (s : CompletedSnapshotGeneric<'T>) =
+        {
+            CallerInfo = s.Caller
+            Replacement = CompletedSnapshotGeneric.replacement s
+        }

WoofWare.Expect/File.fs

@@ -0,0 +1,32 @@
+namespace WoofWare.Expect
+
+open System
+open System.IO
+
+[<RequireQualifiedAccess>]
+module internal File =
+
+    /// Standard attempt at an atomic file write.
+    /// It may fail to be atomic if the working directory somehow spans multiple volumes,
+    /// and of course with external network storage all bets are off.
+    let writeAllLines (lines : string[]) (path : string) : unit =
+        let file = FileInfo path
+
+        let tempFile =
+            Path.Combine (file.Directory.FullName, file.Name + "." + Guid.NewGuid().ToString () + ".tmp")
+
+        try
+            File.WriteAllLines (tempFile, lines)
+            // Atomicity guarantees are undocumented, but on Unix this is an atomic `rename` call
+            // https://github.com/dotnet/runtime/blob/9a4be5b56d81aa04c7ea687c02b3f4e64c83761b/src/libraries/System.Private.CoreLib/src/System/IO/FileSystem.Unix.cs#L181
+            // and on Windows this is an atomic ReplaceFile:
+            // https://github.com/dotnet/runtime/blob/9a4be5b56d81aa04c7ea687c02b3f4e64c83761b/src/libraries/System.Private.CoreLib/src/System/IO/FileSystem.Windows.cs#L92
+            // calls https://github.com/dotnet/runtime/blob/9a4be5b56d81aa04c7ea687c02b3f4e64c83761b/src/libraries/Common/src/Interop/Windows/Kernel32/Interop.ReplaceFile.cs#L12
+            // which calls ReplaceFileW, whose atomicity guarantees are again apparently undocumented,
+            // but 4o-turbo, Opus 4, and Gemini 2.5 Flash all think it's atomic.
+            File.Replace (tempFile, path, null)
+        finally
+            try
+                File.Delete tempFile
+            with _ ->
+                ()

WoofWare.Expect/SnapshotUpdate.fs

@@ -141,7 +141,7 @@ module internal SnapshotUpdate =
         else
             // We need to include enough lines to capture multi-line strings
             // Take a reasonable number of lines after the snapshot line
-            let maxLines = min 50 (lines.Length - startIdx)
+            let maxLines = lines.Length - startIdx
             let relevantLines = lines |> Array.skip startIdx |> Array.take maxLines
 
             let searchText = String.concat "\n" relevantLines
@@ -254,15 +254,19 @@ module internal SnapshotUpdate =
 
     /// <remarks>Example usage:
     ///   <c>updateSnapshotAtLine [|lines-of-file|] 42 "new test output"</c>
-    ///
+    /// <br />
     /// This will find a snapshot call on line 42 like:
-    ///   snapshot "old value"       -> snapshot @"new test output"
-    ///   snapshot @"old value"      -> snapshot @"new test output"
-    ///   snapshot """old value"""   -> snapshot @"new test output"
-    ///   snapshot """multi
-    ///               line"""       -> snapshot """multi
-    ///                                            line"""
-    ///   snapshot "has \"\"\" in it" -> snapshot @"has """""" in it"
+    /// <ul>
+    ///   <li><c>snapshot "old value"</c> -> <c>snapshot @"new test output"</c></li>
+    ///   <li><c>snapshot @"old value"</c> -> <c>snapshot @"new test output"</c></li>
+    ///   <li><c>snapshot """old value"""</c> -> <c>snapshot @"new test output"</c></li>
+    ///   <li><c>snapshot "has \"\"\" in it"</c> -> <c>snapshot @"has """""" in it"</c></li>
+    ///   <li>
+    ///   <code>snapshot """multi
+    ///   line"""</code>       -> <code>snapshot """multi
+    ///   line"""</code>
+    ///   </li>
+    /// </ul>
     /// </remarks>
     let updateSnapshotAtLine (fileLines : string[]) (snapshotLine : int) (newValue : string) : string[] =
         match findSnapshotString fileLines snapshotLine with
@@ -270,3 +274,31 @@ module internal SnapshotUpdate =
             Console.Error.WriteLine ("String literal to update: " + string<StringLiteralInfo> info)
             updateSnapshot fileLines info newValue
         | None -> failwithf "Could not find string literal after snapshot at line %d" snapshotLine
+
+    /// <summary>
+    /// Bulk-apply all the snapshot replacements.
+    /// </summary>
+    /// <param name="fileLines">The original file contents, as an array of lines.</param>
+    /// <param name="sources">The (unsorted) line numbers of the snapshots which need to be replaced, and the replacement value for each.</param>
+    /// <returns>The entire desired new contents of the file, as an array of lines.</returns>
+    let private updateAllLines (fileLines : string[]) (sources : (int * string) seq) : string[] =
+        sources
+        |> Seq.sortByDescending fst
+        |> Seq.fold (fun lines (lineNum, replacement) -> updateSnapshotAtLine lines lineNum replacement) fileLines
+
+    /// <summary>
+    /// Update every failed snapshot in the input, editing the files on disk.
+    /// </summary>
+    let updateAll (sources : CompletedSnapshot seq) : unit =
+        sources
+        |> Seq.groupBy (fun csc -> csc.CallerInfo.FilePath)
+        |> Seq.iter (fun (callerFile, callers) ->
+            let contents = System.IO.File.ReadAllLines callerFile
+
+            let sources =
+                callers |> Seq.map (fun csc -> csc.CallerInfo.LineNumber, csc.Replacement)
+
+            let newContents = updateAllLines contents sources
+
+            File.writeAllLines newContents callerFile
+        )

WoofWare.Expect/SurfaceBaseline.txt

@@ -4,26 +4,34 @@ WoofWare.Expect.Builder.expect' [static property]: [read-only] WoofWare.Expect.E
 WoofWare.Expect.Builder.expectWithMockedFilePath [static method]: (string, int) -> WoofWare.Expect.ExpectBuilder
 WoofWare.Expect.Builder.get_expect [static method]: unit -> WoofWare.Expect.ExpectBuilder
 WoofWare.Expect.Builder.get_expect' [static method]: unit -> WoofWare.Expect.ExpectBuilder
+WoofWare.Expect.CallerInfo inherit obj, implements WoofWare.Expect.CallerInfo System.IEquatable, System.Collections.IStructuralEquatable, WoofWare.Expect.CallerInfo System.IComparable, System.IComparable, System.Collections.IStructuralComparable
+WoofWare.Expect.CallerInfo.Equals [method]: (WoofWare.Expect.CallerInfo, System.Collections.IEqualityComparer) -> bool
+WoofWare.Expect.CompletedSnapshot inherit obj, implements WoofWare.Expect.CompletedSnapshot System.IEquatable, System.Collections.IStructuralEquatable, WoofWare.Expect.CompletedSnapshot System.IComparable, System.IComparable, System.Collections.IStructuralComparable
+WoofWare.Expect.CompletedSnapshot.Equals [method]: (WoofWare.Expect.CompletedSnapshot, System.Collections.IEqualityComparer) -> bool
 WoofWare.Expect.ExpectBuilder inherit obj
 WoofWare.Expect.ExpectBuilder..ctor [constructor]: (string * int)
 WoofWare.Expect.ExpectBuilder..ctor [constructor]: bool
 WoofWare.Expect.ExpectBuilder..ctor [constructor]: WoofWare.Expect.Mode
-WoofWare.Expect.ExpectBuilder.Bind [method]: (WoofWare.Expect.YouHaveSuppliedMultipleSnapshots WoofWare.Expect.ExpectState, unit -> 'U WoofWare.Expect.ExpectState) -> 'U WoofWare.Expect.ExpectState
+WoofWare.Expect.ExpectBuilder.Bind [method]: ('U WoofWare.Expect.ExpectState, unit -> 'U WoofWare.Expect.ExpectState) -> 'U WoofWare.Expect.ExpectState
 WoofWare.Expect.ExpectBuilder.Delay [method]: (unit -> 'T WoofWare.Expect.ExpectState) -> (unit -> 'T WoofWare.Expect.ExpectState)
 WoofWare.Expect.ExpectBuilder.Return [method]: 'T -> 'T WoofWare.Expect.ExpectState
 WoofWare.Expect.ExpectBuilder.Return [method]: unit -> 'T WoofWare.Expect.ExpectState
 WoofWare.Expect.ExpectBuilder.Run [method]: (unit -> 'T WoofWare.Expect.ExpectState) -> unit
-WoofWare.Expect.ExpectBuilder.Snapshot [method]: (unit WoofWare.Expect.ExpectState, string, string option, int option, string option) -> WoofWare.Expect.YouHaveSuppliedMultipleSnapshots WoofWare.Expect.ExpectState
-WoofWare.Expect.ExpectBuilder.SnapshotJson [method]: (unit WoofWare.Expect.ExpectState, string, string option, int option, string option) -> WoofWare.Expect.YouHaveSuppliedMultipleSnapshots WoofWare.Expect.ExpectState
+WoofWare.Expect.ExpectBuilder.Snapshot [method]: ('a WoofWare.Expect.ExpectState, string, string option, int option, string option) -> 'a WoofWare.Expect.ExpectState
+WoofWare.Expect.ExpectBuilder.SnapshotJson [method]: (unit WoofWare.Expect.ExpectState, string, string option, int option, string option) -> 'a WoofWare.Expect.ExpectState
+WoofWare.Expect.ExpectBuilder.WithFormat [method]: ('T WoofWare.Expect.ExpectState, 'T -> string) -> 'T WoofWare.Expect.ExpectState
+WoofWare.Expect.ExpectBuilder.WithJsonDocOptions [method]: ('T WoofWare.Expect.ExpectState, System.Text.Json.JsonDocumentOptions) -> 'T WoofWare.Expect.ExpectState
+WoofWare.Expect.ExpectBuilder.WithJsonSerializerOptions [method]: ('T WoofWare.Expect.ExpectState, System.Text.Json.JsonSerializerOptions) -> 'T WoofWare.Expect.ExpectState
 WoofWare.Expect.ExpectException inherit System.Exception, implements System.Collections.IStructuralEquatable
 WoofWare.Expect.ExpectException..ctor [constructor]: string
 WoofWare.Expect.ExpectException..ctor [constructor]: unit
 WoofWare.Expect.ExpectException.Equals [method]: (System.Exception, System.Collections.IEqualityComparer) -> bool
 WoofWare.Expect.ExpectException.Equals [method]: System.Exception -> bool
 WoofWare.Expect.ExpectException.Message [property]: [read-only] string
-WoofWare.Expect.ExpectState`1 inherit obj, implements 'T WoofWare.Expect.ExpectState System.IEquatable, System.Collections.IStructuralEquatable, 'T WoofWare.Expect.ExpectState System.IComparable, System.IComparable, System.Collections.IStructuralComparable
-WoofWare.Expect.ExpectState`1.Equals [method]: ('T WoofWare.Expect.ExpectState, System.Collections.IEqualityComparer) -> bool
+WoofWare.Expect.ExpectState`1 inherit obj
+WoofWare.Expect.GlobalBuilderConfig inherit obj
+WoofWare.Expect.GlobalBuilderConfig.clearTests [static method]: unit -> unit
+WoofWare.Expect.GlobalBuilderConfig.enterBulkUpdateMode [static method]: unit -> unit
+WoofWare.Expect.GlobalBuilderConfig.updateAllSnapshots [static method]: unit -> unit
 WoofWare.Expect.Mode inherit obj, implements WoofWare.Expect.Mode System.IEquatable, System.Collections.IStructuralEquatable, WoofWare.Expect.Mode System.IComparable, System.IComparable, System.Collections.IStructuralComparable
-WoofWare.Expect.Mode.Equals [method]: (WoofWare.Expect.Mode, System.Collections.IEqualityComparer) -> bool
-WoofWare.Expect.YouHaveSuppliedMultipleSnapshots inherit obj, implements WoofWare.Expect.YouHaveSuppliedMultipleSnapshots System.IEquatable, System.Collections.IStructuralEquatable, WoofWare.Expect.YouHaveSuppliedMultipleSnapshots System.IComparable, System.IComparable, System.Collections.IStructuralComparable
-WoofWare.Expect.YouHaveSuppliedMultipleSnapshots.Equals [method]: (WoofWare.Expect.YouHaveSuppliedMultipleSnapshots, System.Collections.IEqualityComparer) -> bool
+WoofWare.Expect.Mode.Equals [method]: (WoofWare.Expect.Mode, System.Collections.IEqualityComparer) -> bool

WoofWare.Expect/Text.fs

@@ -0,0 +1,6 @@
+namespace WoofWare.Expect
+
+[<RequireQualifiedAccess>]
+module internal Text =
+    let predent (c : char) (s : string) =
+        s.Split '\n' |> Seq.map (sprintf "%c %s" c) |> String.concat "\n"

WoofWare.Expect/WoofWare.Expect.fsproj

@@ -17,7 +17,11 @@
 
     <ItemGroup>
         <Compile Include="AssemblyInfo.fs" />
+        <Compile Include="Text.fs" />
+        <Compile Include="File.fs" />
+        <Compile Include="Domain.fs" />
         <Compile Include="SnapshotUpdate.fs" />
+        <Compile Include="Config.fs" />
         <Compile Include="Builder.fs" />
         <None Include="..\README.md">
           <Pack>True</Pack>

WoofWare.Expect/version.json

@@ -1,5 +1,5 @@
 {
-  "version": "0.2",
+  "version": "0.4",
   "publicReleaseRefSpec": [
     "^refs/heads/main$"
   ],

flake.nix

@@ -65,6 +65,7 @@
           pkgs.alejandra
           pkgs.nodePackages.markdown-link-check
           pkgs.shellcheck
+          pkgs.xmlstarlet
         ];
       };
     });