1 When to use

• Use this skill to answer which changes in a branch or PR are tests and which are not.
• Use the repository script instead of classifying paths by hand. Rust tests are commonly colocated in production .rs files.

2 Run

• Fetch the PR base before relying on origin/master.
• Run from the repository root:

uv run --no-project .claude/skills/frb-categorize-code-diff/categorize_code_diff.py --base origin/master --head HEAD

• Add --json when another tool will consume the result.
• Pass the PR's actual base revision when it is not origin/master.

3 Interpret

• test-only: every changed line is in a dedicated test path or a recognized colocated Rust test region.
• non-test-only: every changed line is outside recognized test code.
• mixed: the file contains both test and non-test changed lines.
• unclassified: the diff cannot be mapped confidently, such as a binary patch.
• Treat the non-test list as conservative. Unknown code is non-test rather than silently counted as test.

4 Reliability

• The script compares base...head, matching GitHub pull request diff semantics.
• Dedicated test paths include test/, tests/, test_fixtures/, and conventional test filenames.
• Rust inline classification recognizes brace-delimited items preceded by #[cfg(test)] or #[test] in both the base and head revisions.
• Re-run after every PR update. Line identities and rename targets may change.
• Inspect mixed files manually before claiming that a PR contains no production changes.

5 Validation

• Run the script tests after changing its classification logic:

PYTHONDONTWRITEBYTECODE=1 uv run --no-project --with pytest --with typer pytest -q .claude/skills/frb-categorize-code-diff/test_categorize_code_diff.py

• Keep PYTHONDONTWRITEBYTECODE=1; otherwise pytest leaves an untracked __pycache__/ inside the skill directory.