There is a description in the pull request which looks relevant to these tests:

> NUnit reflects over the TestCase attribute many times when running tests. To prevent AutoFixture from having to regenerate the values needed for a test multiple times, the results are stored in a static ConcurrentDictionary after the first time.

Is the described behavior a bug in the current implementation? Is it a bug in NUnit (and perhaps we could report it)?

In any case, it looks like these tests are actually testing an implementation detail..