patch.object(type(settings), ATTR, ...) fails on pydantic BaseSettings, patch instance instead

Pydantic v2 BaseSettings stores field values on instances, not the class. unittest.mock.patch.object(type(settings), "FIELD", value) raises AttributeError: <class 'Settings'> does not have the attribute 'FIELD' because the class holds only field descriptors/schema, not values. The working form is patch.object(settings, "FIELD", value) on the module-level singleton, or patch("module.settings.FIELD", value). Verified 2026-04 with pydantic-settings 2.x.

When temporarily overriding a pydantic Settings field in a test, patch the singleton instance directly (patch.object(settings, "FIELD", value)) or use patch("module.path.settings.FIELD", value). Never patch type(settings) / the class.