Add more tests!

[StanFromIreland]

The core infrastructure was added in 82c244b, now it is time to add tests for the remained of scripts.

This process will hopefully find a few bugs we missed, and aid us in refactoring.

[m-aciek]

Related: introduce tests coverage tracking for generation code. With it, it will be easier to track this issue progress.

[BHUVANSH855]

Add more tests! — Initial Investigation

I did a first pass on the current main branch (5fd81e0a5) and ran the existing test suite with coverage.

Current coverage

File	Coverage
completion.py	22%
contribute.py	100%
generate.py	51%
repositories.py	50%
translated_names.py	89%
Total	61%

The main gap is completion.py, especially get_completion(). It has several untested paths around branch fallback, Git errors, historical completion, zero completion, and the 30-day comparison.

There are also no dedicated tests yet for build_warnings.py, generate_build_details.py, or sphinx_lint.py.

While running the suite on Windows, I also hit a couple of portability issues in the existing code (strftime %-d/%-H and implicit file encoding), which aren't covered by the current Ubuntu-only CI.

I’m going to use this to map out the remaining coverage rather than just add tests for test count.