Testing Strategy

Testing Strategy Skill

Detailed rules: See rules/common/testing.md for comprehensive testing standards.

Overview

Comprehensive testing strategy for unit tests, integration tests, coverage analysis, and mock strategies.

Test Types

Test Structure (AAA Pattern)

def test_user_creation():
    # Arrange - set up test data
    user_service = UserService()
    test_data = {"name": "John", "email": "john@example.com"}

    # Act - call the function under test
    result = user_service.create_user(test_data)

    # Assert - verify the result
    assert result.success
    assert result.user.name == "John"

Test Naming Convention

Format: test_<what>_<condition>_<expected> or should <expected> when <condition>

# Good names
def test_login_with_invalid_password_returns_401(): ...
def test_calculate_total_with_empty_cart_returns_zero(): ...
def should_reject_expired_tokens(): ...

# Bad names
def test1(): ...
def test_login(): ...

Unit Test Patterns

Mock Pattern

def test_api_integration():
    mock_client = MockClient()
    mock_client.get.return_value.status_code = 200

    service = APIService(mock_client)
    result = service.get_data()

    mock_client.get.assert_called_once()

Parametrized Tests

@pytest.mark.parametrize("input_val,expected", [
    ("hello", "HELLO"),
    ("world", "WORLD"),
    ("", ""),
])
def test_uppercase(input_val: str, expected: str) -> None:
    assert to_upper(input_val) == expected

Integration Test Patterns

Database Integration

def test_database_operations():
    with TestDatabase() as db:
        user = db.create_user(test_data)
        retrieved = db.get_user(user.id)
        assert retrieved == user

API Integration

def test_api_end_to_end():
    with TestServer(app) as server:
        response = server.post("/api/users", json=test_data)
        assert response.status_code == 201
        assert response.json()["id"] is not None

Mock Strategies

Mock Types

# Mock Response
class MockResponse:
    def __init__(self, json_data, status_code):
        self.json_data, self.status_code = json_data, status_code
    def json(self): return self.json_data

# Mock Database
class MockDatabase:
    def __init__(self): self.data = {}
    def get(self, key): return self.data.get(key)
    def set(self, key, value): self.data[key] = value

Fixtures

# conftest.py
@pytest.fixture
def mock_database(): return MockDatabase()

@pytest.fixture
def sample_user(): return User(name="Alice", email="alice@example.com")

Test Structure

tests/
  unit/test_models.py
  integration/test_api.py
  performance/test_load.py
  conftest.py

pytest Configuration

[tool.pytest.ini_options]
testpaths = ["tests"]
addopts = ["--strict-markers", "--cov=app", "--cov-fail-under=80"]
markers = ["unit", "integration", "performance", "smoke"]

CI/CD Integration

# .github/workflows/tests.yml
name: Tests
on: [push, pull_request]

jobs:
  tests:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - uses: actions/setup-python@v2
      - run: pip install -r requirements.txt pytest pytest-cov
      - run: pytest --cov=app --cov-report=xml
      - uses: codecov/codecov-action@v1

Edge Cases to Test

• Null/None/undefined inputs
• Empty collections, strings, objects
• Boundary values: 0, -1, MAX_INT, empty string
• Unicode: emojis, RTL text, very long strings
• Error paths: network failure, timeout, invalid format

Test Independence Rules

• Each test runs independently
• Tests can run in any order
• No shared mutable state between tests
• Use setup/teardown for common setup
• Clean up: delete temp files, reset singletons

Coverage Standards

Anti-Patterns to Avoid

• Test interdependency: test B passes only if test A runs first
• Excessive mocking: mocking everything = testing nothing
• Testing implementation: changing internals breaks tests
• Slow tests nobody runs: if >5min, developers skip it
• Assert-free tests: a test without assertions is useless

Common Issues & Fixes

Commands

# Run all tests
pytest

# Run with coverage
pytest --cov=app --cov-report=term-missing

# Run specific test types
pytest -m unit
pytest -m integration

# Parallel execution
pytest -n 4