pytest Cheatsheet¶

Installation¶

Platform	Command
pip (All platforms)	`pip install pytest`
Ubuntu/Debian	`sudo apt install python3-pytest`
Fedora/RHEL	`sudo dnf install python3-pytest`
Arch Linux	`sudo pacman -S python-pytest`
macOS (Homebrew)	`brew install pytest`
Windows (Chocolatey)	`choco install pytest`
Virtual Environment	`python -m venv venv && source venv/bin/activate && pip install pytest`
With Common Plugins	`pip install pytest pytest-cov pytest-xdist pytest-mock pytest-html`
Verify Installation	`pytest --version`

Basic Commands¶

Command	Description
`pytest`	Run all tests in current directory and subdirectories
`pytest test_file.py`	Run tests in a specific file
`pytest tests/`	Run all tests in a specific directory
`pytest test_file.py::test_function`	Run a specific test function
`pytest test_file.py::TestClass`	Run all tests in a specific class
`pytest test_file.py::TestClass::test_method`	Run a specific test method in a class
`pytest -v`	Run tests with verbose output (show test names)
`pytest -vv`	Run tests with very verbose output (show full details)
`pytest -q`	Run tests in quiet mode (minimal output)
`pytest -s`	Show print statements and stdout during test execution
`pytest -x`	Stop after first test failure
`pytest --maxfail=3`	Stop after N test failures
`pytest -k "test_user"`	Run tests matching keyword expression
`pytest -k "user and not admin"`	Run tests matching multiple keywords (AND/NOT logic)
`pytest -m "slow"`	Run tests marked with specific marker
`pytest -m "not slow"`	Run tests excluding specific marker
`pytest --collect-only`	Show which tests would be run without executing them
`pytest --lf`	Run only tests that failed in last run (last failed)
`pytest --ff`	Run failed tests first, then others (failed first)
`pytest -l`	Show local variables in tracebacks on failure

Advanced Usage¶

Command	Description
`pytest -n auto`	Run tests in parallel using all available CPU cores (requires pytest-xdist)
`pytest -n 4`	Run tests in parallel with 4 worker processes
`pytest --durations=10`	Show the 10 slowest test durations
`pytest --durations=10 --durations-min=1.0`	Show slowest tests taking at least 1 second
`pytest --cov=myproject`	Run tests with code coverage report (requires pytest-cov)
`pytest --cov=myproject --cov-report=html`	Generate HTML coverage report in htmlcov/ directory
`pytest --cov=myproject --cov-report=term-missing`	Show coverage with missing line numbers in terminal
`pytest --cov=myproject --cov-fail-under=80`	Fail if coverage is below 80%
`pytest --cov-branch`	Include branch coverage analysis
`pytest --junitxml=report.xml`	Generate JUnit XML report for CI/CD integration
`pytest --html=report.html`	Generate HTML test report (requires pytest-html)
`pytest --pdb`	Drop into Python debugger (PDB) on test failures
`pytest --trace`	Drop into PDB at the start of each test
`pytest --setup-show`	Show setup and teardown of fixtures during execution
`pytest --fixtures`	List all available fixtures and their docstrings
`pytest --markers`	List all registered markers
`pytest --tb=short`	Use shorter traceback format
`pytest --tb=line`	Show one line per failure in traceback
`pytest --tb=no`	Disable traceback output
`pytest -W error::DeprecationWarning`	Treat deprecation warnings as errors
`pytest --capture=no`	Disable output capturing (same as -s)
`pytest --timeout=300`	Set timeout of 300 seconds per test (requires pytest-timeout)
`pytest --count=3`	Repeat each test 3 times (requires pytest-repeat)
`pytest --random-order`	Run tests in random order (requires pytest-random-order)
`pytest -ra`	Show short test summary for all tests (passed, failed, skipped, etc.)

Configuration¶

pytest.ini Configuration File¶

Place in project root directory:

[pytest]
# Minimum pytest version required
minversion = 7.0

# Directories to search for tests
testpaths = tests

# Test file patterns
python_files = test_*.py *_test.py

# Test class patterns
python_classes = Test* *Tests

# Test function patterns
python_functions = test_*

# Default command line options
addopts = 
    -ra
    --strict-markers
    --strict-config
    --verbose
    --cov=myproject
    --cov-report=html
    --cov-report=term-missing

# Custom markers
markers =
    slow: marks tests as slow (deselect with '-m "not slow"')
    integration: marks tests as integration tests
    unit: marks tests as unit tests
    smoke: marks tests as smoke tests
    database: marks tests requiring database connection
    api: marks tests for API testing

# Directories to ignore
norecursedirs = .git .tox dist build *.egg venv node_modules

# Warning filters
filterwarnings =
    error
    ignore::UserWarning
    ignore::DeprecationWarning

# Logging configuration
log_cli = true
log_cli_level = INFO
log_cli_format = %(asctime)s [%(levelname)s] %(message)s
log_cli_date_format = %Y-%m-%d %H:%M:%S

pyproject.toml Configuration¶

Modern Python projects using pyproject.toml:

[tool.pytest.ini_options]
minversion = "7.0"
testpaths = ["tests"]
python_files = ["test_*.py", "*_test.py"]
python_classes = ["Test*"]
python_functions = ["test_*"]

addopts = [
    "-ra",
    "--strict-markers",
    "--cov=myproject",
    "--cov-branch",
    "--cov-report=html",
    "--cov-report=term-missing:skip-covered",
    "--cov-fail-under=80",
]

markers = [
    "slow: marks tests as slow",
    "integration: integration tests",
    "unit: unit tests",
    "smoke: smoke tests",
]

filterwarnings = [
    "error",
    "ignore::UserWarning",
]

conftest.py - Shared Fixtures¶

Place in test directory root for shared fixtures:

import pytest

# Session-scoped fixture (runs once per test session)
@pytest.fixture(scope="session")
def database():
    """Provide database connection for entire test session"""
    db = create_database_connection()
    yield db
    db.close()

# Module-scoped fixture (runs once per test module)
@pytest.fixture(scope="module")
def api_client():
    """Provide API client for test module"""
    client = APIClient()
    yield client
    client.cleanup()

# Function-scoped fixture (default, runs for each test)
@pytest.fixture
def sample_data():
    """Provide sample data for testing"""
    return {"id": 1, "name": "Test User"}

# Autouse fixture (automatically used by all tests)
@pytest.fixture(autouse=True)
def reset_state():
    """Reset application state before each test"""
    clear_cache()
    yield
    cleanup_resources()

# Parametrized fixture
@pytest.fixture(params=["sqlite", "postgres", "mysql"])
def db_type(request):
    """Test with multiple database types"""
    return request.param

# Configure pytest hooks
def pytest_configure(config):
    """Add custom configuration"""
    config.addinivalue_line(
        "markers", "custom: custom marker description"
    )

Common Use Cases¶

Use Case 1: Basic Unit Testing¶

# Create test file
cat > test_calculator.py << 'EOF'
def add(a, b):
    return a + b

def test_add():
    assert add(2, 3) == 5
    assert add(-1, 1) == 0
    assert add(0, 0) == 0
EOF

# Run the tests
pytest test_calculator.py -v

Use Case 2: Testing with Fixtures¶

# Create test with fixtures
cat > test_user.py << 'EOF'
import pytest

@pytest.fixture
def user_data():
    return {"username": "testuser", "email": "test@example.com"}

def test_user_creation(user_data):
    assert user_data["username"] == "testuser"
    assert "@" in user_data["email"]
EOF

# Run tests with fixture details
pytest test_user.py -v --setup-show

Use Case 3: Parametrized Testing¶

# Create parametrized tests
cat > test_math.py << 'EOF'
import pytest

@pytest.mark.parametrize("input,expected", [
    (2, 4),
    (3, 9),
    (4, 16),
    (5, 25),
])
def test_square(input, expected):
    assert input ** 2 == expected
EOF

# Run parametrized tests
pytest test_math.py -v

Use Case 4: Integration Testing with Markers¶

# Create tests with markers
cat > test_api.py << 'EOF'
import pytest

@pytest.mark.unit
def test_data_validation():
    assert True

@pytest.mark.integration
def test_api_endpoint():
    # Simulated API test
    assert True

@pytest.mark.slow
@pytest.mark.integration
def test_full_workflow():
    # Long-running test
    assert True
EOF

# Run only unit tests
pytest test_api.py -m unit -v

# Run integration tests excluding slow ones
pytest test_api.py -m "integration and not slow" -v

Use Case 5: Coverage Report Generation¶

# Run tests with coverage and generate reports
pytest --cov=myproject --cov-report=html --cov-report=term-missing

# View coverage report
# HTML report will be in htmlcov/index.html

# Run with coverage threshold
pytest --cov=myproject --cov-fail-under=80

# Generate coverage badge
pytest --cov=myproject --cov-report=term --cov-report=html

Best Practices¶

Use descriptive test names: Name tests with test_ prefix and describe what they test (e.g., test_user_registration_with_valid_email)
Follow AAA pattern: Structure tests with Arrange (setup), Act (execute), Assert (verify) sections for clarity
Use fixtures for setup/teardown: Leverage pytest fixtures instead of setup/teardown methods for better reusability and dependency injection
Mark tests appropriately: Use markers (@pytest.mark.slow, @pytest.mark.integration) to categorize tests and enable selective execution
Keep tests isolated: Each test should be independent and not rely on the state from other tests; use fixtures with appropriate scopes
Use parametrize for similar tests: Instead of writing multiple similar tests, use @pytest.mark.parametrize to test multiple inputs
Configure pytest.ini or pyproject.toml: Set project-wide defaults for test discovery, markers, and command-line options in configuration files
Write focused assertions: Use simple, clear assertions; pytest's introspection shows detailed failure information automatically
Use conftest.py for shared fixtures: Place reusable fixtures in conftest.py files at appropriate directory levels
Run tests frequently: Execute tests during development with pytest -x to stop on first failure for faster feedback
Monitor test coverage: Regularly check coverage reports and aim for 80%+ coverage, but focus on meaningful tests over percentage

Troubleshooting¶

Issue	Solution
Tests not discovered	Ensure files match patterns: `test_.py` or `_test.py`, functions start with `test_`, classes start with `Test`
Import errors in tests	Add empty `__init__.py` files in test directories, or install package in editable mode: `pip install -e .`
Fixture not found	Check fixture is defined in same file or `conftest.py`, verify correct scope, ensure fixture name matches parameter
Tests pass locally but fail in CI	Check for environment-specific dependencies, ensure consistent Python versions, verify all dependencies in `requirements.txt`
Slow test execution	Use `pytest --durations=10` to identify slow tests, consider parallel execution with `pytest -n auto`, mark slow tests with `@pytest.mark.slow`
Coverage not working	Install pytest-cov: `pip install pytest-cov`, ensure source path is correct: `--cov=myproject`, check `.coveragerc` configuration
Markers not recognized	Register markers in `pytest.ini` or `pyproject.toml` under `[tool.pytest.ini_options]`, use `--strict-markers` to catch typos
PDB not working with capture	Use `pytest -s --pdb` to disable output capturing, or use `pytest.set_trace()` instead of `pdb.set_trace()`
Fixtures running in wrong order	Check fixture scope (session > module > class > function), use `@pytest.fixture(autouse=True)` carefully, review dependency chain
Parallel tests failing	Ensure tests are isolated and don't share state, check for race conditions, use proper locking for shared resources
Memory leaks in tests	Use `@pytest.fixture(scope="function")` for proper cleanup, ensure fixtures yield and cleanup properly, check for circular references
Warnings cluttering output	Configure warning filters in `pytest.ini`: `filterwarnings = ignore::DeprecationWarning`, or use `-W` flag: `pytest -W ignore::UserWarning`