Raise CollectError if import test module fails

[omarkohl]

A few tests are still failing and need to be fixed. I will do that and adapt the CHANGELOG if the change makes sense.

I honestly don't see much point in fixing #1426 (but did it because it looked simple enough).

Here's a quick checklist that should be present in PRs:

• Target: for bug or doc fixes, target master; for new features, target features
• Make sure to include one or more tests for your change
• Add yourself to AUTHORS
• Add a new entry to the CHANGELOG (choose any open position to avoid merge conflicts with other PRs)

One of the reasons for failing to import the test module is invalid Python
identifiers in the full package path of the test module.

fix #1426

[nicoddemus]

Thanks! While I agree that this seems like the original user report was a stretch, I don't think it hurts either. 😁

[omarkohl]

I improved the error message a little, fixed failing tests and added a CHANGELOG entry.

I force pushed the branch instead of adding commits to avoid cluttering the repository.

[nicoddemus]

Thanks! The tests are failing because of a minor output detail between Python versions, could you please fix it?

[omarkohl]

Thanks! The tests are failing because of a minor output detail between Python versions, could you please fix it?

Yep I'm on it.

[nicoddemus]

Oh sorry @omarkohl, just now I saw that you did make a new commit. Thanks again!