Update to MTP

[Youssef1313]

This PR updates the repo to use Microsoft.Testing.Platform instead of VSTest. This works with xunit 2 thanks via YTest.MTP.XUnit2 (package that I own - not maintained by xUnit.net or Microsoft).

[AArnott]

oh! Very interesting. This is not the only xunit v2 extension that thus far hasn't moved to MTP for its own internal tests because of the apparent incompatibility. I'll be curious to learn more about how this is achieved.
I may want to rearrange the xml slightly to match what's in Library.Template to avoid merge conflicts down the road as well.

It looks like you're still working on it so I'll hold off reviewing for a while.

Thanks for contributing, @Youssef1313!

[Youssef1313]

oh! Very interesting. This is not the only xunit v2 extension that thus far hasn't moved to MTP for its own internal tests because of the apparent incompatibility. I'll be curious to learn more about how this is achieved.

In simple terms, YTest.MTP.XUnit2 implements an MTP test framework based on the public xunit 2 APIs that allows to run/discover tests. https://github.com/Youssef1313/YTest.MTP.XUnit2/blob/190d316dd771469e4b7b7375d9e351d321df1b9e/src/YTest.MTP.XUnit2/MTPFramework/XUnit2MTPTestFramework.cs is the ITestFramework implementation that I register, and the core logic for reporting test results is in https://github.com/Youssef1313/YTest.MTP.XUnit2/blob/190d316dd771469e4b7b7375d9e351d321df1b9e/src/YTest.MTP.XUnit2/XUnitSinks/MTPExecutionSink.cs

I may want to rearrange the xml slightly to match what's in Library.Template to avoid merge conflicts down the road as well.

It looks like Directory.Packages.props is already not in sync with the current one in Library.Template.

It looks like you're still working on it so I'll hold off reviewing for a while.

It should be green (hopefully) on the current state. I had to update the cloud test script though, which is diverging from Library.Template. It's unfortunate that MTP filtering isn't standardized (xunit.v3 chose to do their own filter command-line options, while MSTest/NUnit keeps the same syntax of the VSTest filter, etc). So as of today, there is unfortunately no way for the cloud test script to do filtering correctly in a way that will be correct for all test frameworks. This will also be quite big problem for solutions that are mixing multiple test frameworks. I opened microsoft/testfx#7160 which I will discuss with the team once I'm back from vacation (or probably a little bit after - depending on the priorities).