Feature: improve unit tests and e2e test for better coverage

[laurentsimon]

there are many tests, so this should be done progressively

[azeemshaikh38]

+1. We really need this. I also think we should make existing tests to be hermetic and non-flaky.

[laurentsimon]

Something we additionally need is e2e tests for the CLI arguments. We need to test things like:
--repo=bla --policy=, --repo=bla --policy=bla --checks=bla, --local=bla --repo=bla, --local=bla --checks=bla, etc. In particular, not all checks are supported when running on a local folder. Also, if checks are explicitly listed, they must be a subset of whose contained in the policy file. Ill add more requirements when we have the GH actions (which adds these additional options) ready.

[spencerschrock]

Given the age I'm going to mark this as done, especially given the unit test work Naveen did last year.