ludo-technologies/python-best-practices/testing

def test_expired_token_is_rejected() -> None:
    # Arrange
    token = make_token(expires_at=YESTERDAY)
    # Act
    result = validate(token)
    # Assert
    assert result.valid is False

# Narrow scope by default
@pytest.fixture
def user() -> User:
    return User(name="alice", email="alice@example.com")
# Factory fixture for varied data
@pytest.fixture
def make_user() -> Callable[..., User]:
    def _make(name: str = "alice", active: bool = True) -> User:
        return User(name=name, email=f"{name}@example.com", active=active)
    return _make

@pytest.mark.parametrize(
    ("email", "valid"),
    [
        pytest.param("a@example.com", True, id="simple-address"),
        pytest.param("a@sub.example.com", True, id="subdomain"),
        pytest.param("no-at-sign", False, id="missing-at"),
        pytest.param("", False, id="empty-string"),
    ],
)
def test_email_validation(email: str, valid: bool) -> None:
    assert is_valid_email(email) is valid

# Mock the external boundary with a faithful interface.
# `mocker` requires the pytest-mock plugin; with stdlib only,
# use unittest.mock.patch as a decorator or context manager.
def test_notifies_on_signup(mocker: MockerFixture) -> None:
    send = mocker.patch("app.signup.email_client.send", autospec=True)
    signup(email="alice@example.com")
    send.assert_called_once_with(to="alice@example.com", template="welcome")
# monkeypatch for environment variables
def test_reads_api_key(monkeypatch: pytest.MonkeyPatch) -> None:
    monkeypatch.setenv("API_KEY", "test-key")
    assert load_config().api_key == "test-key"