TestMethodAttribute.Execute currently returns TestResult[] but all known implementations return a single result.

This seems to currently be an API flaw that has been present only for historical reasons where previously parameterized tests where handled in DataTestMethodAttribute:

So, DataTestMethodAttribute had to return multiple test results. The design is now very different and the whole DataTestMethodAttribute isn't actually required now. So I feel like the API should change here and return a single TestResult for simplicity.

Still, we need to be very careful with changes here, in case there are valid use cases for returning multiple results (but I don't see that right now).