Exception System.InvalidCastException thrown when running NUnit and FsCheck tests

[sideeffffect]

Hello, I have a trivial project started from ProjectScaffold.
I have a test file tests/FSharpHello.Tests/Tests.fs like this:

module FSharpHello.Tests

open FSharpHello
open NUnit.Framework
open FsUnit
open FsCheck
open FsCheck.NUnit

[<Test>]
let ``hello returns 42`` () =
  Library.hello 42 |> should equal 42

[<Property>]
let ``hello alwaysreturns 42``(x:int) =
  Library.hello x = 42

and I get error like this

mono  /home/ondra/Projects/FSharpHello/packages/NUnit.Runners/tools/nunit-console.exe "-nologo" "-noshadow" "-labels" "/home/ondra/Projects/FSharpHello/tests/FSharpHello.Tests/bin/Release/FSharpHello.Tests.dll" "-xml:TestResults.xml" 
WARNING: The runtime version supported by this application is unavailable.
Using default runtime: v4.0.30319
ProcessModel: Default    DomainUsage: Single
Execution Runtime: mono-4.0
Unhandled Exception:
System.InvalidCastException: Cannot cast from source type to destination type.

Server stack trace: 
  at (wrapper xdomain-dispatch) NUnit.Core.RemoteTestRunner:Load (object,byte[]&,byte[]&)

Exception rethrown at [0]: 

  at (wrapper xdomain-invoke) NUnit.Core.RemoteTestRunner:Load (NUnit.Core.TestPackage)
  at NUnit.Util.TestDomain.Load (NUnit.Core.TestPackage package) [0x00000] in <filename unknown>:0 
Running build failed.
Error:
Fake.UnitTestCommon+FailedTestsException: NUnit test failed (156).
  at Fake.NUnitSequential.NUnit (Microsoft.FSharp.Core.FSharpFunc`2 setParams, IEnumerable`1 assemblies) [0x00000] in <filename unknown>:0 
  at FSI_0001.Build+clo@137-11.Invoke (Microsoft.FSharp.Core.Unit _arg7) [0x00000] in <filename unknown>:0 
  at Fake.TargetHelper+targetFromTemplate@155[Microsoft.FSharp.Core.Unit].Invoke (Microsoft.FSharp.Core.Unit unitVar0) [0x00000] in <filename unknown>:0 
  at Fake.TargetHelper.runSingleTarget (Fake.TargetTemplate`1 target) [0x00000] in <filename unknown>:0 

this exception is thrown only when I run the build script ./build.sh from shell. when build or run tests in MonoDevelop, everything seems ok.

is this a bug in FAKE? if not, where is the problem?

[TheAngryByrd]

This issue was also reported on FsCheck:
fscheck/FsCheck#115

A possible work around is to specify -domain:None flag to the nunit console runner, however FAKE doesn't seem to give you an option.

https://github.com/fsharp/FAKE/blob/master/src/app/FakeLib/UnitTest/NUnit/Common.fs

type NUnitDomainModel = 
    /// No domain is created - the tests are run in the primary domain. This normally requires copying the NUnit assemblies into the same directory as your tests.
    | DefaultDomainModel
    /// A test domain is created - this is how NUnit worked prior to version 2.4
    | SingleDomainModel
    /// A separate test domain is created for each assembly
    | MultipleDomainModel with
    member x.ParamString =
        match x with
        | DefaultDomainModel -> ""
        | SingleDomainModel -> "Single"
        | MultipleDomainModel -> "Multiple"

DefaultDomainModel claims to specify "No domain", but doesn't specify None in the ParamString method which seems to default to Single.

I think Default should specify "None" as per Nunit docs but probably needs to Default to single as to not break things.

[sideeffffect]

this bug is still present with FAKE (4.0.2)

you can see the log from travis

[TheAngryByrd]

@sideeffffect Make sure in your build.fsx you set the domain to DefaultDomainModel to specify no domain.

[sideeffffect]

I get the error

error FS1129: The type 'NUnitParams' does not contain a field 'DefaultDomainModel'

[TheAngryByrd]

Whoops sorry, Copy paste is not my friend.

Target "RunTests" (fun _ ->
    !! testAssemblies
    |> NUnit (fun p ->
        { p with
            DisableShadowCopy = true
            Domain = NUnitDomainModel.DefaultDomainModel 
            TimeOut = TimeSpan.FromMinutes 20.
            OutputFile = "TestResults.xml" })
)

[sideeffffect]

great, that worked, seems to be fixed now. thank you!

[DavidTheBugWriter]

Not fixed for me. My build.fsx has:

Target "RunTests" (fun _ ->
    !! testAssemblies

    |> NUnit (fun p ->

        { p with

            DisableShadowCopy = true

            Domain = NUnitDomainModel.NoDomainModel 

            TimeOut = TimeSpan.FromMinutes 20.

            OutputFile = "TestResults.xml" })
)

and my tests are:

open NUnit.Framework
open FsCheck.NUnit
[< Property>]
let ``Reverse of reverse of a list is the original list ``(xs:list<int>) =
                    List.rev(List.rev xs) = xs
[< Test>]
let ``hello returns 42`` () =
  let result = Library.hello 42
  printfn "%i" result
  Assert.AreEqual(42,result)`

Still gives me the error

Tests Not Run:

1. NotRunnable : secondproject.Tests.Reverse of reverse of a list is the original list
   Test method has non-void return type, but no result is expected

FAKE version is 4.17.1

[rprouse]

Are changes required for this from the NUnit team? If so, please report to nunit/nunit#731

[matthid]

@DavidTheBugWriter Feel free to open a new issue if needed.