Atomic file writes (#12)

.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

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

@@ -1,21 +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

@@ -270,7 +270,7 @@ type ExpectBuilder (mode : Mode) =
                 let lines = File.ReadAllLines state.Caller.FilePath
                 let oldContents = String.concat "\n" lines
                 let lines = SnapshotUpdate.updateSnapshotAtLine lines state.Caller.LineNumber actual
-                File.WriteAllLines (state.Caller.FilePath, lines)
+                File.writeAllLines lines state.Caller.FilePath
                 failwith ("Snapshot successfully updated. Previous contents:\n" + oldContents)
 
         match CompletedSnapshotGeneric.passesAssertion state with

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
@@ -300,5 +300,5 @@ module internal SnapshotUpdate =
 
             let newContents = updateAllLines contents sources
 
-            System.IO.File.WriteAllLines (callerFile, newContents)
+            File.writeAllLines newContents callerFile
         )

WoofWare.Expect/WoofWare.Expect.fsproj

@@ -18,6 +18,7 @@
     <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" />

flake.nix

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