Tests inconsistently used individual file manager context managers (PyprojectTOMLManager, SetupCFGManager, etc.) instead of the unified files_manager(). This made tests fragile and inconsistent—files_manager() locks all managers atomically, which is the correct pattern.

Test file changes (~270 replacements across 28 files)

• Simple cases: with change_cwd(tmp_path), PyprojectTOMLManager(): → with change_cwd(tmp_path), files_manager():
• Multi-manager cases: collapsed PyprojectTOMLManager(), UVTOMLManager() into single files_manager()
• as binding cases: moved manager instantiation into the body since files_manager() already locks the class-level state:

# Before
with change_cwd(tmp_path), PyprojectTOMLManager() as mgr:
    mgr[["tool", "uv", "environments"]] = []

# After
with change_cwd(tmp_path), files_manager():
    mgr = PyprojectTOMLManager()
    mgr[["tool", "uv", "environments"]] = []

• Updated imports: added files_manager, removed now-unused manager imports

Enforcement hook

Added a pygrep-language prek hook no-bare-managers-in-tests matching ^\s*with\b.*Manager\( in tests/, excluding the three base manager infrastructure test files (test_ini_io_.py, test_toml_io_.py, test_yaml_io_.py) that legitimately use custom My*Manager() subclasses.