[AhmethanKalenderoglu]

Description

Adds tests/spec_tools/test_codemods.py with unit tests for CommentReplaceCommand, StringReplaceCommand and SetConstantCommand, using LibCST's CodemodTest like the issue suggests. RemoveDocstringCommand already has tests in test_new_fork.py, so I left those where they are.

SetConstantCommand needs FullyQualifiedNameProvider, and CodemodTest doesn't set up a cache for it, so those tests write the module to a temp directory and pass a FullRepoManager through context_override.

While writing these I noticed that SetConstantCommand on a tuple assignment like X, Y = 1, 2 replaces the whole right hand side (X, Y = 3), while X = Y = 1 raises NotImplementedError. No fork defines constants that way right now so I didn't touch it here, but I can send a fix separately.

Related Issues or PRs

Fixes #2196

Checklist

• Ran fast static checks to avoid CI fails, see Code Standards & Verifying Changes: just static
• PR title has the form <type>(<area>): <description>, where <type> and <area> come from an appropriate C-<type>, respectively A-<area>, label. The title should match the target squash commit message.

Ran ruff, mypy and codespell on the new file. The full just static needs the optimized group, which doesn't build on my Windows machine.

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[spencer-tb]

Thanks for the PR! Pushed a small trim of the tests and the tuple unpacking fix, LGTM :D

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.98%. Comparing base (e91a505) to head (f34e02c).
⚠️ Report is 6 commits behind head on forks/bogota.

Additional details and impacted files

@@              Coverage Diff              @@
##           forks/bogota    #3776   +/-   ##
=============================================
  Coverage         94.98%   94.98%           
=============================================
  Files               673      673           
  Lines             40831    40831           
  Branches           3747     3747           
=============================================
  Hits              38785    38785           
  Misses             1429     1429           
  Partials            617      617           

Flag	Coverage Δ
unittests	94.98% <ø> (ø)

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