hypothesis and coverage conflict to mis-report some test coverage

[exarkun]

There is a test method which runs and passes but is marked as not covered:

https://codecov.io/gh/LeastAuthority/txkube/commit/feaf0ebf226ae3a9d9a3b988edb57cf8505098e1#D1-363

This may be related to https://github.com/HypothesisWorks/hypothesis-python/issues/997