Jest Best Practices: Why You Should Use jest.clearAllMocks() in afterEach

In automated testing, particularly when using Jest, managing mock states effectively is critical for ensuring reliable, independent, and accurate test results. One frequent point of confusion is where to place Jest’s cleanup methods, especially jest.clearAllMocks().

Here’s why placing jest.clearAllMocks() in afterEach is considered best practice:

Why afterEach is the Recommended Place

✅ Isolates Each Test Case

When mocks are cleared after each test, every test begins with a clean slate. This isolation ensures that no leftover mock behavior from a previous test affects the outcomes of subsequent tests, guaranteeing independent execution.

✅ Prevents State Leakage

Using jest.clearAllMocks() in afterEach ensures that tests do not unintentionally reuse mock implementations or internal states. This avoids subtle and hard-to-trace bugs caused by lingering mock states from previously run tests, which could lead to false positives or negatives.

✅ Semantically Consistent Teardown

Using afterEach aligns with standard teardown procedures in testing frameworks. Just as you'd typically close database connections or clear timers in afterEach, it is logical to also clear mocks at this stage.

Recommended Implementation

Here’s how your Jest test setup should look:

beforeEach(async () => {
  module = await createTestingModule(...);
  service = module.get(...);
});

afterEach(() => {
  jest.clearAllMocks(); // Ensures cleanup after every test
});

🚫 What to Avoid

Placing jest.clearAllMocks() in the beforeEach might sometimes seem sufficient, but it’s not a foolproof strategy:

beforeEach(() => {
  jest.clearAllMocks(); // NOT recommended
});

This method might inadvertently allow the very first test to be impacted by mocks set in previous tests if the test file or environment is reused, particularly in scenarios involving complex mocking or modules resetting.

Quick Reference Table

Placement Recommended? Reason afterEach ✅ Yes Clears test pollution after each test beforeEach 🚫 No Risks state leakage into the first test

Final Thoughts

Always prefer placing jest.clearAllMocks() in afterEach. It keeps your tests isolated, predictable, and easy to debug, ultimately enhancing the reliability and maintainability of your testing suite.