polyfactory

Polyfactory is a typed mock-data factory library: declare ModelFactory[T] (or DataclassFactory, MsgspecFactory, AttrsFactory, TypedDictFactory) and .build() returns a populated instance of T. The matching factory base inspects the model's annotations and supported constraints so tests do not need hand-written happy-path fixtures.

In Litestar projects, polyfactory's pytest plugin is the canonical way to feed TestClient.post(...) / AsyncTestClient.put(...) payloads. The companion skill litestar:litestar-testing covers the request side.

Code Style Rules

• PEP 604 unions: T | None, never Optional[T].
• One factory per model. Don't reuse a factory across unrelated models — clarity beats DRY when the test fails at 3am.
• Pick the right factory base by backend: ModelFactory (Pydantic), DataclassFactory, MsgspecFactory, AttrsFactory, TypedDictFactory. A mismatched base raises ConfigurationException.
• Prefer register_fixture over hand-rolled @pytest.fixture wrappers. Call it in a pytest-discovered test module or conftest.py so the injected fixture is collected.

Quick Reference

Picking the right factory base