Write Tests

Use this skill when a change needs tests or when existing tests look too coupled to implementation details.

Read TESTING.md before writing or reviewing non-trivial tests. It is the shared behavior-focused testing policy, also used by commit. Read AGENTS.md for the repo's coding standards. If the repo has package- or module-specific testing docs, read the nearest one for local commands, markers, fakes, mocks, and numerical tolerances before choosing a test style.

Workflow

1. Find existing tests for the touched behavior before creating a new file.
2. Check for repo-specific testing rules for commands, markers, fakes, mocks, and numerical tolerances.
3. Name the behavior that should fail if the code is wrong.
4. Write the smallest test that observes that behavior through a public API, structured output, persisted state, or real side effect.
5. Prefer a regression test before the fix when fixing a bug. Ensure the test fails before implementing the bug fix.
6. Keep test setup realistic but small. Use fixtures and parameterization to remove duplication.
7. Run the narrow test first, then the relevant package test command. Before a PR, run the repo lint entry point required by AGENTS.md.

Default Commands

• Run the repo's test command over the test directories your change touches (e.g. uv run pytest -m 'not slow').
• For package-specific commands, use the relevant package testing doc.

For PR preparation, run infra/pre-commit.py --changed-files --fix or infra/pre-commit.py --all-files --fix as appropriate. Do not replace it with uv run pre-commit.