Sinon
Sinon is a standalone JavaScript library for creating test spies, stubs, and mocks in unit tests. It provides utilities to isolate and control dependencies, such as functions, objects, or server requests, enabling developers to test code in isolation without relying on external systems. It is commonly used with testing frameworks like Mocha, Jest, or Jasmine to enhance test reliability and coverage.
Developers should learn Sinon when writing unit tests for JavaScript applications to mock external dependencies, such as API calls, database interactions, or complex objects, ensuring tests are fast, deterministic, and focused on specific code units. It is particularly useful in test-driven development (TDD) or behavior-driven development (BDD) workflows to simulate edge cases, control function behavior, and verify interactions without executing real-world side effects.