Constructor fails inside an array under xUnit

[ImaginaryDevelopment]

type AccidentDataModel (accidentId,displayText,code) as self =
    inherit FSharp.ViewModule.ViewModelBase()

    let accidentId      = self.Factory.Backing  (<@ self.AccidentID @>,         accidentId)
    let displayText     = self.Factory.Backing  (<@ self.DisplayText @>,        displayText)
    let code            = self.Factory.Backing  (<@ self.Code @>,               code)

    new () = AccidentDataModel(0,String.Empty,String.Empty)

    member x.AccidentID with get() = accidentId.Value and set v = accidentId.Value <- v
    member x.DisplayText with get() = displayText.Value and set v = displayText.Value <- v
    member x.Code with get() = code.Value and set v = code.Value <- v

Succeeding test

open global.Xunit
open FsCheck
open FsCheck.Xunit
            [<Property>]
            let createAccidentModelTest x y z = 
                let model = Pm.Dal.DataModels.AccidentDataModel(x,y,z)
                Assert.NotNull model 
                Assert.Equal(x,model.AccidentID)
                Assert.Equal(y, model.DisplayText)
                Assert.Equal(z, model.Code)

Failing test for both cases 1, and 100

            [<Theory>]
            [<InlineData(1)>]
            [<InlineData(100)>]
            let createAccidentList length = 
                //generate a single instance of 't
                let generateOne() = FsCheck.Arb.generate<'a>.Sample(1,1) |> Seq.head
                let generateAdm () = Pm.Dal.DataModels.AccidentDataModel(generateOne() , generateOne(), generateOne())
                let items = 
                    [0..length-1]
                    |> Seq.map (ignore >> generateAdm)
                    |> Array.ofSeq
                Assert.NotNull items
                Assert.Equal(items.Length,length)

exception

Test Name: Pm.Tests.IntegrationTests.IntegrationTestModule+DataAccess+Accidents.createAccidentList(length: 100)
Test FullName: Pm.Tests.IntegrationTests.IntegrationTestModule+DataAccess+Accidents.createAccidentList
Test Source: C:\TFS\PracticeManagement\dev\PracticeManagement\Pm.Tests\Integration.XUnit.fs : line 263
Test Outcome: Failed
Test Duration: 0:00:00.229

Result StackTrace:
at Microsoft.FSharp.Core.LanguagePrimitives.IntrinsicFunctions.FailInit()
at FSharp.ViewModule.Internal.ViewModelUntyped.Validate(String propertyName)
at FSharp.ViewModule.ValidationTracker.validatePropertiesInternal(String propertyName)
Result Message: System.InvalidOperationException : The initialization of an object or value resulted in an object or value being accessed recursively before it was fully initialized.

[ReedCopsey]

@ImaginaryDevelopment Would it be possible to make a standalone reproducible example of this? Ideally, something that reproduces in FSI or simliar?

I'm not sure what's happening, but it'd be nice to narrow down what causes this to go crazy, since it's not obvious from your code above.

[ImaginaryDevelopment]

stand-alone repro solution
FsXamlXUnit.bug.zip

F# library project, that uses VS xunit runners via run all tests.

[ImaginaryDevelopment]

any news on this?

[ReedCopsey]

So, finally managed to track this down.

@ImaginaryDevelopment It turns out the problem is that xUnit is setting up a synchronization context that's wholly inappropriate for UI work in this case.

You can work around it by removing the context in your test:

[<Theory>]
[<InlineData(1)>]
[<InlineData(100)>]
let createAccidentList length = 
    System.Threading.SynchronizationContext.SetSynchronizationContext(null)
    let generateAdm () = AccidentDataModel(generateOne() , generateOne(), generateOne())
    let items = 
        [0..length-1]
        |> Seq.map (fun _ -> generateAdm())
        |> Array.ofSeq
    Assert.NotNull items
    Assert.Equal(items.Length,length)

If you remove this, then it works perfectly.

[allykzam]

Just spent about an hour trying to figure out the same InvalidOperationException result in a unit test before seeing this; I got as far as changing this line to:

let errorTracker = ValidationTracker(self.RaiseErrorChanged, propertyChanged.Publish, (fun (_) -> Seq.empty), errorRelatedProperties)

and this also clears up the error. Is there some other "proper" way that the ViewModelUntyped ctor should be referencing the abstract member Validate that wouldn't cause this? Or should I just be cleaning up the SynchronizationContext as well?