Implement tests

[jeffwright13]

(using Pytest's pytester module)

https://raphael.codes/blog/test-suites-for-pytest-plugins/

See https://docs.pytest.org/en/6.2.x/writing_plugins.html#testing-plugins https://docs.pytest.org/en/latest/contributing.html#writing-tests https://docs.pytest.org/en/latest/reference/reference.html?highlight=pytester#pytest.Pytester

[jeffwright13]

One idea: make a test run, and compare the final summary line output metrics vs. individual internal statistics for P, F, S, XP, XF, etc.

[jeffwright13]

External packages with lots of tests to run against: alive-progress quantiphy pyexpect rich

[jeffwright13]

test for --collect-only