tests: Start linting tests

I believe we should enable linting (tox -e lint) for new test files (maybe even for some recent additions). Possibly some exceptions are needed but in general I think the tests would be better if they were linted.

Good start for this would be test_updater_with_simulator.py and repository_simulator.py: it’s new code and files are small so the changes are easy – the real job is figuring out how to select what to lint… Possible options:

• separate directory for legacy (unlinted) tests?
• define list of linted files in tox.ini / setup.cfg ? (I don’t like this one as it means default for new files is no lint)
• define list of files excluded from lint in tox.ini & setup.cfg ?
• some other strategy?

[joshuagl]

Splitting tests across multiple directories may make sense, but I think the right combination of simple and not prone to error is a list of files excluded from lint? That way, new test files are linted and there’s no ambiguity about where to place new tests.

Also, the no-lint list gets shorter as we replace/remove existing tests.

[MVrachev]

TODO items left to close this issue:

• address pylint and mypy warnings | #1657
• add configuration to actually start linting the tests