# Pytest

> Best practices for writing and organizing tests with pytest including fixtures, parametrize, and plugins. Use when this capability is needed.

- Skill: `tomevault-io/pytest-10` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add tomevault-io/pytest-10`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/pytest-10/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: tomevault-io (https://skillmd.com/u/tomevault-io)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/tomevault-io/pytest-10

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# Skill: pytest

Best practices for writing and organizing tests with pytest including fixtures, parametrize, and plugins.

## When to Use

Apply this skill when writing and organizing tests with pytest — fixtures, parametrize, markers, plugins, and test structure.

## Test Organization

- Place tests in a `tests/` directory mirroring the source structure.
- Name test files `test_<module>.py` and test functions `test_<behavior>()`.
- Group related tests in classes only when they share fixtures/setup.

## Fixtures

- Define fixtures at the narrowest scope needed (`function` > `class` > `module` > `session`).
- Use `conftest.py` for shared fixtures; put it at the appropriate directory level.
- Prefer factory fixtures over complex fixture inheritance.
- Use `yield` fixtures for setup/teardown; prefer `tmp_path` over `tempfile`.

## Parametrize

- Use `@pytest.mark.parametrize` for data-driven tests with multiple inputs.
- Give test IDs (`ids=...`) for readable test output.
- Combine `parametrize` with fixtures for cross-product testing.

## Assertions

- Use plain `assert` statements — pytest rewrites them for clear failure messages.
- Use `pytest.raises(ExceptionType, match=...)` for exception testing.
- Use `pytest.approx()` for floating-point comparisons.

## Plugins

- Common plugins: `pytest-cov`, `pytest-mock`, `pytest-asyncio`, `pytest-xdist`, `pytest-timeout`.
- Use `pytest-mock`'s `mocker` fixture over raw `unittest.mock.patch`.

## Pitfalls

- Don't use `session`-scoped fixtures for mutable state.
- Don't assert on implementation details — test observable behavior.
- Avoid test interdependence; each test should be runnable in isolation.

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> Source: [jukanntenn/glm-plan-usage](https://github.com/jukanntenn/glm-plan-usage) — distributed by [TomeVault](https://tomevault.io).
<!-- tomevault:4.0:skill_md:2026-06-16 -->