Python Library Testing
Quick Start
bash
pytest # Run tests pytest --cov=my_library # With coverage pytest -x # Stop on first failure pytest -k "test_encode" # Run matching tests
Pytest Configuration
toml
# pyproject.toml [tool.pytest.ini_options] testpaths = ["tests"] addopts = "-ra -q --cov=my_library --cov-fail-under=85" [tool.coverage.run] branch = true source = ["src/my_library"]
Test Structure
code
tests/ ├── conftest.py # Shared fixtures ├── test_encoding.py └── test_decoding.py
Essential Patterns
Basic test:
python
def test_encode_valid_input():
result = encode(37.7749, -122.4194)
assert isinstance(result, str)
assert len(result) == 12
Parametrization:
python
@pytest.mark.parametrize("lat,lon,expected", [
(37.7749, -122.4194, "9q8yy"),
(40.7128, -74.0060, "dr5ru"),
])
def test_known_values(lat, lon, expected):
assert encode(lat, lon, precision=5) == expected
Fixtures:
python
@pytest.fixture
def sample_data():
return [(37.7749, -122.4194), (40.7128, -74.0060)]
def test_batch(sample_data):
results = batch_encode(sample_data)
assert len(results) == 2
Mocking:
python
def test_api_call(mocker):
mocker.patch("my_lib.client.fetch", return_value={"data": []})
result = my_lib.get_data()
assert result == []
Exception testing:
python
def test_invalid_raises():
with pytest.raises(ValueError, match="latitude"):
encode(91.0, 0.0)
For detailed patterns, see:
- •FIXTURES.md - Advanced fixture patterns
- •HYPOTHESIS.md - Property-based testing
- •CI.md - CI/CD test configuration
Test Principles
| Principle | Meaning |
|---|---|
| Independent | No shared state between tests |
| Deterministic | Same result every run |
| Fast | Unit tests < 100ms each |
| Focused | Test behavior, not implementation |
Checklist
code
Testing: - [ ] Tests exist for public API - [ ] Edge cases covered (empty, boundary, error) - [ ] No external service dependencies (mock them) - [ ] Coverage > 85% - [ ] Tests run in CI