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