Add more coverage

[blink1073]

• Add more coverage for extension app and files handler (which was actually broken).
• Get windows-specific coverage

[codecov]

Codecov Report

Base: 75.14% // Head: 75.63% // Increases project coverage by +0.48% 🎉

Coverage data is based on head (ad66cb9) compared to base (830c87f).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1069      +/-   ##
==========================================
+ Coverage   75.14%   75.63%   +0.48%     
==========================================
  Files          63       63              
  Lines        8225     8222       -3     
  Branches     1635     1634       -1     
==========================================
+ Hits         6181     6219      +38     
+ Misses       1624     1576      -48     
- Partials      420      427       +7     

Impacted Files	Coverage Δ
jupyter_server/files/handlers.py	85.45% <100.00%> (+50.97%)	⬆️
jupyter_server/services/kernels/handlers.py	61.61% <0.00%> (-1.02%)	⬇️
jupyter_server/extension/serverextension.py	87.05% <0.00%> (+7.19%)	⬆️
jupyter_server/extension/utils.py	84.21% <0.00%> (+15.78%)	⬆️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report at Codecov.
📢 Do you have feedback about the report comment? Let us know in this issue.

[blink1073]

Question: should we deprecate the previously broken FilesHandler class?

[blink1073]

We're going to keep the FileHandler class, since it is used by default for ContentsManager, while FileContentsManager uses the AuthenticatedFileHandler class. Both are actually authenticated, which is an unfortunate naming.