Added [LabsUITestMethod] attribute and source generator

[Arlodotexe]

Background

Closes #143

This PR adds the [LabsUITestMethod] attribute and source generator. When the source generator sees this attribute, it will:

• Generate a test method that always invokes on the UI thread
• If needed, pulls type info from the constructor, and provides a control instance.
• Works with both synchronous and asynchronous method.

Basic usage

Synchronous, with control:

[LabsUITestMethod]
public void MyControl_TestSomething(MyControl testControl)
{
    var scrollViewer = testControl.FindDescendant<ScrollViewer>();

    Assert.AreEqual(200, scrollViewer.HorizontalOffset);
}

Synchronous, without control:

[LabsUITestMethod]
public void SimpleTest()
{
    // Runs on the UI thread
    Assert.AreEqual(1, 1);
}

Asynchronous, with control:

[LabsUITestMethod]
public async Task MyControl_TestSomething(MyControl testControl)
{
    var contentDialog = testControl.FindDescendant<ContentDialog>();

    await contentDialog.ShowAsync();

    Assert.IsTrue(contentDialog.IsPrimaryButtonEnabled);
}

Asynchronous, without control:

[LabsUITestMethod]
public async Task PropertySizer_TestChangeBinding()
{
    // Runs on the UI thread
    await Task.Delay(1000);
    Assert.AreEqual(1, 1);
}

[michael-hawker]

@Arlodotexe should we add an example test to the template as well to show this being used for folks?

[michael-hawker]

Few small things and some suggestions for more tests to shore things up.

[michael-hawker]

Oh, also really confused why the extension isn't working as it's a bit odd for us to re-implement this. Can you sync with @Sergio0694 quick sometime for 10 minutes on a call and trying and diagnose/go through the issue?

[Arlodotexe]

I'll set that up in the morning, see if we can pick out exactly what went wrong. I can't repro the issue yet, but we can use the code from before this PR.

[Sergio0694]

Is it only this overload taking a Func<Task<T>> that's causing issues, or all of them?

[michael-hawker]

Looks like a test failure isn't getting caught by the MSTest infrastructure at the moment now with the new attributed method? We should have a case to try where use the attribute to expect a known exception and then throw that exception and make sure that works...

[michael-hawker]

Hmm, the error may be getting eaten in the CI as well, as I just see the general abort message as well: https://github.com/CommunityToolkit/Labs-Windows/runs/6914398636?check_suite_focus=true#step:15:227 - hopefully we can fix the error bubbling, and then get more info out of the CI about the failure... though I'll be sad if we can't run the input injection APIs in the CI... 😥

[Arlodotexe]

Looks like a test failure isn't getting caught by the MSTest infrastructure at the moment now with the new attributed method? We should have a case to try where use the attribute to expect a known exception and then throw that exception and make sure that works...

That's odd. I suppose we should add this to #160, but that means this PR can't be closed until that one is.

[Arlodotexe]

@michael-hawker Sergio and I weren't able to reproduce the issue with the EnqueueAsync extension in the toolkit. It's been reverted and test now succeed and fail as expected. Feel free to rebase your branch as needed.

[Sergio0694]

> Test fail for no reason
> Write a workaround
> Test pass
> Remove workaround
> Test pass
> *shrug*
> LGTM!

[michael-hawker]

@Arlodotexe don't think the build ran as there's conflicts to resolve?

[michael-hawker]

Looking good, will see how the CI does (and I'll try on my other branch to see what happens too). Just a few file-scoped namespaces that were missed.

[Arlodotexe]

@Arlodotexe don't think the build ran as there's conflicts to resolve?

I ran into some issues with Visual Studio refusing to build after resolving conflicts, complaining about missing types. Should be good now.

[michael-hawker]

My other PR helped to exercise this a bit more too. I'll do a quick check locally, but then I think we'll be good!

[michael-hawker]

Yay, I see the failures now in VS! 🎉🎉🎉

Seems to be working great. Awesome job! Thanks @Arlodotexe!