[all] [qa] [oslo] Usage of testtools?

Hi folks, Most OpenStack projects use testtools/fixtures/unittest2 for unit tests. It was immensely helpful in Python 2 times, but I wonder if we should migrate away now. I've hit at least these three bugs: https://github.com/testing-cabal/testtools/issues/235 https://github.com/testing-cabal/testtools/issues/275 https://github.com/testing-cabal/testtools/issues/144 We can invest time in fixing them, but I wonder if we should just migrate to the standard unittest (and move oslotest to it) now that we require Python >= 3.6. Thoughts? Dmitry