Use pytest fixtures effectively

Tests should use pytest fixtures to improve organization, promote test isolation, and avoid code duplication. Fixtures provide a clean way to set up test dependencies, manage test state, and create reusable test components.

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Tests should use pytest fixtures to improve organization, promote test isolation, and avoid code duplication. Fixtures provide a clean way to set up test dependencies, manage test state, and create reusable test components.

Key principles:

  • Use fixtures for test setup instead of global variables to prevent test pollution
  • Monkeypatch environment variables and dependencies within fixtures
  • Extract repetitive test code into parameterized fixtures
  • Use session or module-level fixtures for expensive setup operations
  • Store test constants in fixtures or dedicated constant files

Example:

# Before: Using global variables and repetitive code
counter_holder = {"counter": 0, "parsing_counter": 0}  # Risky global state

def get_client_with_custom_config(config_value):
    app = FastAPI(config=config_value)
    return TestClient(app)

def test_feature_a():
    client = get_client_with_custom_config("value1")
    # Test implementation...

def test_feature_b():
    client = get_client_with_custom_config("value2")
    # Test implementation...

# After: Using pytest fixtures
@pytest.fixture
def counter():
    return {"counter": 0, "parsing_counter": 0}  # Isolated for each test

@pytest.fixture
def client(request):
    config_value = request.param
    app = FastAPI(config=config_value)
    return TestClient(app)

@pytest.mark.parametrize("client", ["value1", "value2"], indirect=True)
def test_features(client, counter):
    # Test implementation using client and counter...

Using fixtures properly improves test isolation, prevents unexpected side effects between tests, and makes test maintenance easier by centralizing common setup logic.

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