Allow async test methods for UITestMethod on UWP and WinUI - #5297

Uhm, how does this address #740? The former is about being able to use datarows with UITests, this PR on the other hand allows using async on tests right?

Marcel W. (@marcelwgn) The original issue description is inaccurate. Based on the comments/discussions there, the real issue is really just UITestMethodAttribute deadlocking. Using parameterized tests does not require DataTestMethodAttribute, and so we should not introduce UIDataTestMethodAttribute as it doesn't serve any purpose.

So the following test should work then?

[UITestMethod]
[DataRow(0)]
[DataRow(1)]
[DataRow(2)]
public void TestMethod2(int index)
{
    var grid = new Grid
    {
        MinWidth = index
    };

    grid.UpdateLayout();

    Assert.AreEqual(index, grid.ActualWidth);
}

Because when I run it in Visual Studio, I get the following issue:

    Cannot run test method 'App8.UnitTest1.TestMethod2': Test data doesn't match method parameters. Either the count or types are different.
Test expected 1 parameter(s), with types 'Int32',
but received 0 argument(s), with types ''.

The thread in that issue evolved to providing a workaround to that missing capability using async tests that would essentially implement the behaviour that UITestMethod should support, but that requires async which is not supported. I disagree that the original issue description is misleading, the above sample does not work so there still is no support for this. ALlowing async would just allow for a workaround to work.

It's supposed to work. I'll check why it doesn't work, but that wasn't what I understood from the follow-up comments.

Marcel W. (@marcelwgn) This should be working if you are using the latest MSTest. I could repro only with really old versions of MSTest that are not supported.