Testing Patterns

Testing Patterns

Expert guidance for writing effective Python tests with pytest.

Quick Start

Basic Test Structure

import pytest
from src.services.task_manager import TaskManager

class TestTaskManager:
    """Group related tests in classes."""

    def test_create_task_with_valid_title(self) -> None:
        """Test names describe expected behavior."""
        manager = TaskManager(storage=InMemoryStorage())

        task = manager.create_task("Buy groceries")

        assert task.title == "Buy groceries"
        assert task.completed is False

    def test_create_task_raises_on_empty_title(self) -> None:
        """Test error conditions explicitly."""
        manager = TaskManager(storage=InMemoryStorage())

        with pytest.raises(ValidationError, match="Title cannot be empty"):
            manager.create_task("")

Fixtures for Dependencies

import pytest

@pytest.fixture
def storage() -> InMemoryStorage:
    """Create fresh storage for each test."""
    return InMemoryStorage()

@pytest.fixture
def task_manager(storage: InMemoryStorage) -> TaskManager:
    """Fixtures can depend on other fixtures."""
    return TaskManager(storage=storage)

def test_create_task(task_manager: TaskManager) -> None:
    task = task_manager.create_task("Test")
    assert task.id is not None

Test Organization

Directory Structure

tests/
├── conftest.py          # Shared fixtures
├── unit/                # Isolated unit tests
│   ├── conftest.py      # Unit-specific fixtures
│   ├── test_task_manager.py
│   └── test_storage.py
├── integration/         # Component integration
│   ├── conftest.py
│   └── test_agent_workflow.py
└── contract/            # API contract tests
    └── test_agent_contracts.py

Naming Conventions

Coverage Target: 80%+

# Run with coverage
pytest --cov=src --cov-report=term-missing --cov-fail-under=80

# Generate HTML report
pytest --cov=src --cov-report=html

Coverage priorities:

1. Business logic (services, managers) - 90%+
2. Data models and validation - 85%+
3. Error handling paths - 80%+
4. Edge cases and boundaries - covered

Reference Guides

For detailed patterns, see:

• Pytest Setup: See references/pytest-setup.md for configuration, markers, and CLI options
• Mocking Patterns: See references/mocking-patterns.md for mocks, stubs, fakes, and dependency injection testing
• Async Testing: See references/async-testing.md for pytest-asyncio patterns and async fixtures
• TDD Workflow: See references/tdd-workflow.md for Red-Green-Refactor cycle and best practices
• Integration Testing: See references/integration-testing.md for multi-component and workflow testing