Improve coverage

[jordiferrero]

Description of the change

Add tests for px_to_nm_grating_solver

Progress of the PR

• [x] added tests,
• [x] check coverage and correct until perfect
• [x] ready for review.

[codecov-commenter]

Codecov Report

Base: 97.81% // Head: 99.45% // Increases project coverage by +1.63% :tada:

Coverage data is based on head (65f08de) compared to base (34fb15c). Patch has no changes to coverable lines.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #145 +/- ## ========================================== + Coverage 97.81% 99.45% +1.63% ========================================== Files 11 11 Lines 550 550 ========================================== + Hits 538 547 +9 + Misses 12 3 -9 ``` | [Impacted Files](https://codecov.io/gh/LumiSpy/lumispy/pull/145?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LumiSpy) | Coverage Δ | | |---|---|---| | [lumispy/signals/luminescence\_spectrum.py](https://codecov.io/gh/LumiSpy/lumispy/pull/145/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LumiSpy#diff-bHVtaXNweS9zaWduYWxzL2x1bWluZXNjZW5jZV9zcGVjdHJ1bS5weQ==) | `98.31% <0.00%> (+3.37%)` | :arrow_up: | | [lumispy/signals/cl\_spectrum.py](https://codecov.io/gh/LumiSpy/lumispy/pull/145/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LumiSpy#diff-bHVtaXNweS9zaWduYWxzL2NsX3NwZWN0cnVtLnB5) | `100.00% <0.00%> (+5.08%)` | :arrow_up: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LumiSpy). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LumiSpy)

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[jordiferrero]

@jlaehne Can't seem to see why coverage is not 100%... which lines/files are causing it?

[jlaehne]

It was three lines in remove_background_from_file (exceptions and warnings). I added a commit to ignore them as we want to deprecate that function anyway.

[jlaehne]

100%: https://app.codecov.io/github/LumiSpy/lumispy/pull/145

[jordiferrero]

Thanks. Silly question... but how did you commit to my personal branch whist doing a PR?

[jlaehne]

Good question, it just offered me to open a PR or commit directly and even though I expected it not to work I tried the direct commit.