2789152331
2.9 KiB
WoofWare.Whippet.Plugin.InterfaceMock
This is a Whippet plugin for defining mocks for interfaces.
It is a copy of the corresponding Myriad HttpClient plugin in WoofWare.Myriad, taken from commit d59ebdfccb87a06579fb99008a15f58ea8be394e.
Usage
Define a file like Client.fs:
type IPublicType =
abstract Mem1 : string * int -> string list
abstract Mem2 : string -> int
In your fsproj:
<Project>
<ItemGroup>
<Compile Include="Client.fs" />
<Compile Include="GeneratedClient.fs">
<WhippetFile>Client.fs</WhippetFile>
<WhippetParamIPublicType>InterfaceMock</WhippetParamIPublicType>
</Compile>
</ItemGroup>
<ItemGroup>
<!-- Development dependencies, hence PrivateAssets="all". Note `WhippetPlugin="true"`. -->
<PackageReference Include="WoofWare.Whippet.Plugin.InterfaceMock" WhippetPlugin="true" Version="" />
<PackageReference Include="WoofWare.Whippet" Version="" PrivateAssets="all" />
</ItemGroup>
</Project>
(This plugin follows a standard convention taken by WoofWare.Whippet.Plugin plugins,
where you use Whippet parameters with the same name as each input type,
whose contents are a !-delimited list of the generators which you wish to apply to that input type.)
The generator produces a type like this:
/// Mock record type for an interface
type internal PublicTypeMock =
{
Mem1 : string * int -> string list
Mem2 : string -> int
}
static member Empty : PublicTypeMock =
{
Mem1 = (fun x -> raise (System.NotImplementedException "Unimplemented mock function"))
Mem2 = (fun x -> raise (System.NotImplementedException "Unimplemented mock function"))
}
interface IPublicType with
member this.Mem1 (arg0, arg1) = this.Mem1 (arg0, arg1)
member this.Mem2 (arg0) = this.Mem2 (arg0)
What's the point?
Reflective mocking libraries like Foq in my experience are a rich source of flaky tests. The Grug-brained developer would prefer to do this without reflection, and this reduces the rate of strange one-in-ten-thousand "failed to generate IL" errors. But since F# does not let you partially update an interface definition, we instead stamp out a record, thereby allowing the programmer to use F#'s record-update syntax.
Features
You may supply an isInternal : bool argument:
<Compile Include="GeneratedClient.fs">
<WhippetFile>Client.fs</WhippetFile>
<WhippetParamIPublicType>InterfaceMock(false)</WhippetParamIPublicType>
</Compile>
By default, we make the resulting record type at most internal (never public),
since this is intended only to be used in tests;
but you can instead make it public by setting the false boolean.