PY-TEST0003 · parametrization_candidate_group_count

Count safe sibling-test groups that differ only in literal values.

This is a deterministic rule for python. Read its implementation.

Definition

Compare direct sibling test functions within the same module or class. Preserve the callable kind, fixture parameter names, argument defaults, annotations, decorators, marks, control-flow nodes, operators, and call targets. Replace body literals with typed slots, then report a group only when at least minimum_cases tests have the same remaining syntax and every case has a distinct literal vector. The defaults set minimum_cases to three and maximum_cases to nine.

Evidence

Each finding spans the candidate group, names every test, and measures both case count and the number of literal positions that vary. The rule reports an opportunity and does not rewrite test names or invent parameter IDs. The value is the number of qualifying sibling groups rather than the number of tests in them.

Exceptions

Already parametrized tests, tests with docstring scenarios, exception contexts, explicit try or raise statements, external assignment, and common filesystem or monkeypatch side effects abstain. Different fixtures, marks, control flow, call targets, or literal types form different shapes. Exact duplicate bodies are not parametrization candidates. Ruff PT006, PT007, and PT014 remain responsible for parametrization syntax and duplicate existing cases. Ten or more homogeneous examples belong to PY-TEST0017, which asks for one generated property instead.

Examples

Bad

def test_status_ok(client):
    assert client.get("/ok").status_code == 200

def test_status_missing(client):
    assert client.get("/missing").status_code == 404

def test_status_denied(client):
    assert client.get("/denied").status_code == 403

Good

@pytest.mark.parametrize(
    ("path", "status"),
    [("/ok", 200), ("/missing", 404), ("/denied", 403)],
)
def test_status(client, path, status):
    assert client.get(path).status_code == status

References

• Cites “pytest documentation”, parametrizing fixtures and test functions. Open reference
• Cites “pytest documentation”, parametrization examples. Open reference
• Cites Ruff PT014 pytest-duplicate-parametrize-test-cases. Open reference