test: add tests for slackdeps.NewFs()

[mwbrooks]

Summary

This pull request adds test coverage to slackdeps.NewFs(). Easy review! 🕺🏻 💃🏻

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 63.33%. Comparing base (775c7ef) to head (6915315).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #104      +/-   ##
==========================================
+ Coverage   63.29%   63.33%   +0.03%     
==========================================
  Files         211      211              
  Lines       22282    22282              
==========================================
+ Hits        14104    14112       +8     
+ Misses       7087     7083       -4     
+ Partials     1091     1087       -4     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[zimeg]

@mwbrooks 📝 🔬 ✨ Wow!

This is a nice test to have for all future enhancements and changes around file handling - thank you for making this file 🙏 ✨

[mwbrooks]

Thanks @zimeg! It feels strange putting up such a small PR with minimal test coverage impact, but having the file exists allows future tests to be added easier. 🦠 🔬 🧑‍🔬