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

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 code
• python-async-patterns - Async test patterns (pytest-asyncio)

Testing specific frameworks:

• python-fastapi-patterns - TestClient, API testing
• python-database-patterns - Database fixtures, transactions