[dduugg]

Summary

Three tests in tests/validate_files_test.rs named valid_project/ruby/app/unowned.rb, which doesn't exist. valid_project has to validate cleanly, so it has no unowned file. The tests passed only because a path that doesn't exist is reported as unowned, so they covered that case rather than an unowned file.

Found by @perryqh in #126.

Why

The tests didn't test what their names say. They would also have started failing if nonexistent paths were ever skipped, as #126 proposed.

Changes

• A new valid_project_with_unowned_file helper copies valid_project to a temp dir, writes ruby/app/unowned.rb there, and stages it.
• test_validate_with_unowned_file, test_validate_with_mixed_files and test_generate_and_validate_with_unowned_file use it.
• Each test now checks the whole output (Unowned files detected:\n ruby/app/unowned.rb\n), so the mixed test also checks that ruby/app/models/payroll.rb isn't reported.

#126 pointed these tests at invalid_project instead. That fixture's CODEOWNERS is empty, so every file there is reported as unowned, and the mixed test couldn't tell an owned file from an unowned one.

Test plan

• cargo fmt --all -- --check, cargo clippy --all-targets --all-features -- -D warnings and cargo test pass (306 passed, the 3 existing ignores).
• Mutation check: with validate_files temporarily changed to skip nonexistent paths, the three old tests fail and the new ones pass.