We recently came across this situation, while we were trying to integrate unit testing for one of the applications into VSTS build definition. So strangely enough, all of the test cases were passed but still the task failed:

When we went through logs, we have observed that vsts test task was also trying to parse the Microsoft.VisualStudio*.dll files:

Since the name of the dll starts with Microsoft.VisualStudio, it was easily guessable that this dll was written by Microsoft and as such there was no need for us to test this dll. Now why it was testing those dlls is for something, we needed to look into.

If we look at the default configuration for test task, it would tries to test all assemblies that would have the test name in there and exception for files required by test adapter itself:

The solution was simply to remove the unwanted dlls from test assemblies list:

Once we did that, the build was green again. At this time, it did not checked those dlls and there was no error to report: