flake8-pytest-style

Common errors

• PT001 use @pytest.fixture over @pytest.fixture()

  cause After upgrading to `flake8-pytest-style` v2.0.0+, the default for `pytest-fixture-no-parentheses` was inverted. It now prefers `@pytest.fixture` without parentheses when no arguments are passed.
  fix Change `@pytest.fixture()` to `@pytest.fixture` in your code, or set `pytest-fixture-no-parentheses = false` in your `flake8` configuration to revert to the old behavior.

• PT013 found incorrect import of pytest, use simple 'import pytest' instead

  cause You are using `from pytest import ...` (e.g., `from pytest import fixture`) which `flake8-pytest-style` discourages.
  fix Replace specific imports from `pytest` with `import pytest` and then use `pytest.fixture`, `pytest.mark`, etc.

• PT028 default values in test functions

  cause A test function parameter has a default value, which conflicts with pytest's fixture injection mechanism. Pytest will use the default value instead of the fixture.
  fix Remove the default value from the test function parameter. For example, change `def test_foo(bar=42):` to `def test_foo(bar):`.

• F401 'my_fixture' imported but unused

  cause This is a standard `flake8` (PyFlakes) error, often seen when importing pytest fixtures from a separate file (not `conftest.py`) into your test module. Fixtures are used by injection, not direct calls, making the import appear 'unused' to `flake8`.
  fix The recommended approach is to define reusable fixtures in a `conftest.py` file or use `pytest_plugins = [...]` in `conftest.py` to load them. If you must import, add `# noqa: F401` to the import line to suppress the warning.

Warnings

• breaking Version 2.0.0 (released 2024-04-01) inverted the default values for `pytest-fixture-no-parentheses` (PT001) and `pytest-mark-no-parentheses` (PT023). This change aligns with the official pytest style, but may introduce many new violations upon upgrade.
  Fix: If you experience new PT001 or PT023 violations, you may need to explicitly configure these options in your `flake8` configuration (e.g., `setup.cfg`, `pyproject.toml`) to match your preferred style, or update your code to include/remove parentheses as per the new default.
• breaking The minimum Python version requirement has increased across minor and major versions. Version 2.0.0 requires Python >=3.8.1, version 2.1.0 requires Python >=3.9, and version 2.2.0 requires Python >=3.10.
  Fix: Ensure your project's Python environment meets the minimum version requirement for the `flake8-pytest-style` version you are using. Update your Python environment if necessary.
• gotcha Rules PT004 (fixture without return value should have leading underscore) and PT005 (fixture returning value should not have leading underscore) have been noted by the Ruff linter team (a popular alternative to flake8) as potentially not aligning with all pytest 'best practices'.
  Fix: While `flake8-pytest-style` still reports these, consider if these specific rules fit your project's conventions. You can selectively ignore them via `flake8` configuration if they conflict with your established patterns or other linter's recommendations.
• gotcha Rule PT028 warns against defining default values for parameters in test functions (e.g., `def test_foo(bar=42):`). Pytest's behavior is to use the default value instead of injecting a fixture if one is defined for that parameter, leading to unexpected test behavior.
  Fix: Remove default values from test function parameters that are intended to receive fixtures. Fixtures should be injected without an explicit default.

Install

• pip install flake8-pytest-style Install latest version

Imports

• pytest
  wrong:

  from pytest import fixture, mark

  correct:

  import pytest

  The PT013 rule discourages 'from pytest import ...' in favor of a simple 'import pytest' to avoid implicit imports and make dependencies clearer.

Quickstart

Install the plugin, then run `flake8` as you normally would. The plugin automatically integrates with flake8 to check pytest-related style issues in your project.

import os

# Create a dummy test file
with open('test_example.py', 'w') as f:
    f.write("""
import pytest

@pytest.fixture
def my_fixture(scope='function'): # PT001, PT003
    return 1

def test_example(my_fixture): # PT004
    assert my_fixture == 1

@pytest.mark.parametrize(('val'), [1,2]) # PT023, PT006
def test_parametrized_bad_style(val=10): # PT028
    assert val > 0

def test_raises():
    with pytest.raises(Exception):
        pass # PT010, PT011, PT012
""")

# Run flake8 with the plugin enabled
# flake8 automatically discovers installed plugins
print("\n--- Running flake8 ---")
os.system("flake8 test_example.py")

# Clean up
os.remove('test_example.py')