Python pytest Patterns
Modern pytest patterns for effective testing.
Basic Test Structure
import pytest
def test_basic():
"""Simple assertion test."""
assert 1 + 1 == 2
def test_with_description():
"""Descriptive name and docstring."""
result = calculate_total([1, 2, 3])
assert result == 6, "Sum should equal 6"
Fixtures
import pytest
@pytest.fixture
def sample_user():
"""Create test user."""
return {"id": 1, "name": "Test User"}
@pytest.fixture
def db_connection():
"""Fixture with setup and teardown."""
conn = create_connection()
yield conn
conn.close()
def test_user(sample_user):
"""Fixtures injected by name."""
assert sample_user["name"] == "Test User"
Fixture Scopes
@pytest.fixture(scope="function") # Default - per test
@pytest.fixture(scope="class") # Per test class
@pytest.fixture(scope="module") # Per test file
@pytest.fixture(scope="session") # Entire test run
Parametrize
@pytest.mark.parametrize("input,expected", [
(1, 2),
(2, 4),
(3, 6),
])
def test_double(input, expected):
assert double(input) == expected
# Multiple parameters
@pytest.mark.parametrize("x", [1, 2])
@pytest.mark.parametrize("y", [10, 20])
def test_multiply(x, y): # 4 test combinations
assert x * y > 0
Exception Testing
def test_raises():
with pytest.raises(ValueError) as exc_info:
raise ValueError("Invalid input")
assert "Invalid" in str(exc_info.value)
def test_raises_match():
with pytest.raises(ValueError, match=r".*[Ii]nvalid.*"):
raise ValueError("Invalid input")
Markers
@pytest.mark.skip(reason="Not implemented yet")
def test_future_feature():
pass
@pytest.mark.skipif(sys.platform == "win32", reason="Unix only")
def test_unix_feature():
pass
@pytest.mark.xfail(reason="Known bug")
def test_buggy():
assert broken_function() == expected
@pytest.mark.slow
def test_performance():
"""Custom marker - register in pytest.ini."""
pass
Mocking
from unittest.mock import Mock, patch, MagicMock
def test_with_mock():
mock_api = Mock()
mock_api.get.return_value = {"status": "ok"}
result = mock_api.get("/endpoint")
assert result["status"] == "ok"
@patch("module.external_api")
def test_with_patch(mock_api):
mock_api.return_value = {"data": []}
result = function_using_api()
mock_api.assert_called_once()
pytest-mock (Recommended)
def test_with_mocker(mocker):
mock_api = mocker.patch("module.api_call")
mock_api.return_value = {"success": True}
result = process_data()
assert result["success"]
conftest.py
# tests/conftest.py - Shared fixtures
import pytest
@pytest.fixture(scope="session")
def app():
"""Application fixture available to all tests."""
return create_app(testing=True)
@pytest.fixture
def client(app):
"""Test client fixture."""
return app.test_client()
Quick Reference
| Command | Description |
|---|
pytest | Run all tests |
pytest -v | Verbose output |
pytest -x | Stop on first failure |
pytest -k "test_name" | Run matching tests |
pytest -m slow | Run marked tests |
pytest --lf | Rerun last failed |
pytest --cov=src | Coverage report |
pytest -n auto | Parallel (pytest-xdist) |
Additional Resources
./references/fixtures-advanced.md - Factory fixtures, autouse, conftest patterns./references/mocking-patterns.md - Mock, patch, MagicMock, side_effect./references/async-testing.md - pytest-asyncio patterns./references/coverage-strategies.md - pytest-cov, branch coverage, reports./references/integration-testing.md - Database fixtures, API testing, testcontainers./references/property-testing.md - Hypothesis framework, strategies, shrinking./references/test-architecture.md - Test pyramid, organization, isolation strategies
Scripts
./scripts/run-tests.sh - Run tests with recommended options./scripts/generate-conftest.sh - Generate conftest.py boilerplate
Assets
./assets/pytest.ini.template - Recommended pytest configuration./assets/conftest.py.template - Common fixture patterns
See Also
Related Skills:
python-typing-patterns - Type-safe test codepython-async-patterns - Async test patterns (pytest-asyncio)
Testing specific frameworks:
python-fastapi-patterns - TestClient, API testingpython-database-patterns - Database fixtures, transactions