Expand io test coverage

[ghiggi]

Prework

• I understand and agree to this repository's code of conduct.
• I understand and agree to this repository's contributing guidelines.
• I have already submitted an issue or discussion thread to discuss my idea with the maintainers.

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Documentation
• Tutorial
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

The PR fulfills these requirements:

• It's submitted to the branch named as follow :
  • Fix a bug: bugfix-<some_key>-<word>
  • Improve the doc: doc-<some_key>-<word>
  • Improve a tutorial tutorial-<some_key>-<word>
  • Add a new feature: feature-<some_key>-<word>
  • Refactor some code: refactor-<some_key>-<word>
  • Optimize some code: optimize-<some_key>-<word>
• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)
• Don't forget to link PR to issue if you are solving one.
• All tests are passing.
• New/updated tests are included

I

[coveralls]

coverage: 64.695% (+3.0%) from 61.695%
when pulling 25bc688 on add_multiple_downloads
into 59a1b48 on main.

[codecov]

Codecov Report

Attention: 9 lines in your changes are missing coverage. Please review.

Comparison is base (59a1b48) 61.69% compared to head (25bc688) 64.69%.

Files	Patch %	Lines
gpm_api/io/ges_disc.py	57.14%	6 Missing ⚠️
gpm_api/io/download.py	95.83%	2 Missing ⚠️
gpm_api/io/checks.py	96.29%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #37      +/-   ##
==========================================
+ Coverage   61.69%   64.69%   +3.00%     
==========================================
  Files          62       62              
  Lines        5498     5529      +31     
==========================================
+ Hits         3392     3577     +185     
+ Misses       2106     1952     -154     

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