---
id: NickCrew/Claude-Cortex/python-testing-patterns
version: "f1b02200"
license: MIT
install: manual
updated: 2026-06-29
---

# python-testing-patterns — Learn to build reliable test suites in Python using pytest, fixtures, and mocking strategies. This skill covers unit and integration testing, test organization, async testing, and coverage measurement. Discover patterns for parametrized tests, external dependency mocking, and test-driven development workflows.

Publisher: NickCrew · Stars: 23 · Updated: 2026-06-29

Install (manual): `git clone https://github.com/NickCrew/Claude-Cortex`

## SKILL.md

# Python Testing Patterns

Comprehensive guide to implementing robust testing strategies in Python using pytest, fixtures, mocking, parameterization, and property-based testing.

## When to Use This Skill

- Writing unit tests for Python functions and classes
- Setting up comprehensive test suites and infrastructure
- Implementing test-driven development (TDD) workflows
- Creating integration tests for APIs, databases, and services
- Mocking external dependencies and third-party services
- Testing async code and concurrent operations
- Implementing property-based testing with Hypothesis
- Setting up CI/CD test automation
- Debugging failing tests and improving test coverage

## Core Concepts

**Test Discovery**: Files matching `test_*.py` or `*_test.py`, functions starting with `test_`

**Fixtures**: Reusable test resources with setup and teardown
- Scopes: `function` (default), `class`, `module`, `session`
- Composition: Build complex fixtures from simple ones
- Share via `conftest.py` for project-wide availability

**Assertions**: Use `assert` statements, `pytest.raises()` for exceptions

**Organization**: Separate `unit/`, `integration/`, `e2e/` directories

## Quick Reference

Load detailed references for specific topics:

| Task | Reference File |
|------|----------------|
| Pytest basics, test structure, AAA pattern | `skills/python-testing-patterns/references/pytest-fundamentals.md` |
| Fixtures, scopes, setup/teardown, conftest.py | `skills/python-testing-patterns/references/fixtures.md` |
| Parametrization, multiple test cases | `skills/python-testing-patterns/references/parametrized-tests.md` |
| Mocking, patching, unittest.mock, pytest-mock | `skills/python-testing-patterns/references/mocking.md` |
| Async tests, pytest-asyncio, event loops | `skills/python-testing-patterns/references/async-testing.md` |
| Property-based testing, Hypothesis, strategies | `skills/python-testing-patterns/references/property-based-testing.md` |
| Monkeypatch, environment variables, attributes | `skills/python-testing-patterns/references/monkeypatch.md` |
| Test structure, markers, conftest.py patterns | `skills/python-testing-patterns/references/test-organization.md` |
| Coverage measurement, reports, thresholds | `skills/python-testing-patterns/references/coverage.md` |
| Database, API, Redis, message queue testing | `skills/python-testing-patterns/references/integration-testing.md` |
| Best practices, test quality, fixture design | `skills/python-testing-patterns/references/best-practices.md` |

## Workflow

### 1. Basic Test Setup
```python
# test_example.py
import pytest

def test_something():
    """Descriptive test name."""
    # Arrange
    expected = 5

    # Act
    result = 2 + 3

    # Assert
    assert result == expected
```

**Run tests:**
```bash
pytest                    # Run all tests
pytest -v                 # Verbose output
pytest tests/unit/        # Specific directory
pytest -k "test_user"     # Match pattern
pytest -m unit            # Run marked tests
```

### 2. Using Fixtures
```python
@pytest.fixture
def sample_data():
    """Provide test data."""
    data = {"key": "value"}
    yield data
    # Cleanup if needed

def test_with_fixture(sample_data):
    assert sample_data["key"] == "value"
```

### 3. Parametrized Tests
```python
@pytest.mark.parametrize("input,expected", [
    (2, 4),
    (3, 9),
    (4, 16),
])
def test_square(input, expected):
    assert input ** 2 == expected
```

### 4. Mocking External Dependencies
```python
from unittest.mock import patch

@patch("module.external_api_call")
def test_with_mock(mock_api):
    mock_api.return_value = {"status": "ok"}

    result = my_function()

    assert result["status"] == "ok"
    mock_api.assert_called_once()
```

### 5. Coverage Measurement
```bash
pytest --cov=src --cov-report=term-missing
pytest --cov=src --cov-report=html
pytest --cov=src --cov-fail-under=80
```

### 6. Test Configuration
**pytest.ini:**
```ini
[pytest]
testpaths = tests
python_files = test_*.py
addopts = -v --strict-markers --cov=src
markers =
    unit: Unit tests
    integration: Integration tests
    slow: Slow tests
```

## Common Patterns

**Exception testing:**
```python
with pytest.raises(ValueError, match="error message"):
    function_that_raises()
```

**Async testing:**
```python
@pytest.mark.asyncio
async def test_async_function():
    result = await async_operation()
    assert result is not None
```

**Temporary files:**
```python
def test_file_operation(tmp_path):
    test_file = tmp_path / "test.txt"
    test_file.write_text("content")
    assert test_file.read_text() == "content"
```

**Markers for test selection:**
```python
@pytest.mark.slow
@pytest.mark.integration
def test_database_operation():
    pass
```

## Common Mistakes

1. **Not using fixtures**: Repeating setup code across tests
   - Solution: Create fixtures in conftest.py

2. **Tests depending on order**: Global state pollution
   - Solution: Ensure test independence with proper fixtures

3. **Over-mocking**: Mocking internal implementation
   - Solution: Mock only external boundaries (APIs, databases)

4. **Missing edge cases**: Only testing happy path
   - Solution: Test boundary conditions, errors, and invalid inputs

5. **Slow tests**: Running full integration tests frequently
   - Solution: Separate unit/integration, use markers, optimize fixtures

6. **Ignoring coverage gaps**: Not measuring test coverage
   - Solution: Use pytest-cov and track metrics

7. **Poor test names**: Generic names like `test_1()`
   - Solution: Use descriptive names: `test_<behavior>_<condition>_<expected>`

8. **No cleanup**: Resources not released
   - Solution: Use fixtures with proper teardown (yield pattern)

## Resources

- **pytest**: https://docs.pytest.org/
- **unittest.mock**: https://docs.python.org/3/library/unittest.mock.html
- **pytest-asyncio**: Testing async code
- **pytest-cov**: Coverage reporting
- **pytest-mock**: pytest wrapper for mock
- **Hypothesis**: https://hypothesis.readthedocs.io/
- **pytest-xdist**: Parallel test execution
- **testcontainers**: Docker containers for testing


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