testing

Testing Patterns

Testing strategies and patterns for building reliable, maintainable code with comprehensive test coverage.

When to Use This Skill

• Writing new tests
• Setting up test infrastructure
• Debugging failing tests
• Improving test coverage
• Following TDD methodology
• Writing integration tests

Test Structure

AAA Pattern (Arrange, Act, Assert)

import { describe, it, expect, beforeEach } from 'vitest';

describe('TaskService', () => {
  let service: TaskService;
  let mockDb: MockDatabase;

  beforeEach(() => {
    // Shared setup
    mockDb = createMockDatabase();
    service = new TaskService(mockDb);
  });

  it('should create a task with default priority', async () => {
    // Arrange - set up test data
    const outcomeId = 'outcome-123';
    const title = 'Implement feature';
    
    // Act - execute the code under test
    const task = await service.createTask({ outcomeId, title });
    
    // Assert - verify the results
    expect(task.id).toBeDefined();
    expect(task.title).toBe(title);
    expect(task.priority).toBe(3);  // default
    expect(task.status).toBe('pending');
  });

  it('should throw when outcome does not exist', async () => {
    // Arrange
    const invalidOutcomeId = 'nonexistent';
    
    // Act & Assert
    await expect(
      service.createTask({ outcomeId: invalidOutcomeId, title: 'Test' })
    ).rejects.toThrow('Outcome not found');
  });
});

Test Naming Convention

// Format: should [expected behavior] when [condition]

describe('SessionManager', () => {
  // Good names - clear and specific
  it('should start session when outcome has no blockers', () => {});
  it('should throw SessionActiveError when session already running', () => {});
  it('should emit progress events during task execution', () => {});
  it('should cleanup resources when session is stopped', () => {});
  
  // Bad names - vague or implementation-focused
  it('test start', () => {});  // What does it test?
  it('calls processTask', () => {});  // Testing implementation, not behavior
  it('works correctly', () => {});  // What is "correct"?
});