Advanced JS Mocking Patterns

소개

This skill provides specialized guidance for mastering complex testing scenarios in JavaScript and TypeScript using frameworks like Jest and Vitest. It equips developers with the patterns necessary to mock entire modules, create partial spies for existing objects, and control time with fake timers for asynchronous logic. By enforcing best practices in mock lifecycle management and highlighting common anti-patterns, it ensures that unit and integration tests remain isolated, reliable, and maintainable across both frontend and backend environments.

주요 기능

• Precise control over asynchronous logic with fakeTimers and time advancement
• Detection and prevention of common mocking anti-patterns
• Advanced partial mocking and spy implementations using spyOn
• Standardized mock lifecycle management to prevent state leakage between tests
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• Automated module mocking for Jest and Vitest environments

사용 사례

• Isolating side effects in legacy code via strategic partial mocking
• Mocking external API clients like Axios or Fetch to isolate service logic
• Testing debounced or throttled functions by manipulating virtual time