How to change mock implementation on a per single test basis?

by

Use mockFn.mockImplementation(fn).

import { funcToMock } from './somewhere';
jest.mock('./somewhere');

beforeEach(() => {
  funcToMock.mockImplementation(() => { /* default implementation */ });
  // (funcToMock as jest.Mock)... in TS
});

test('case that needs a different implementation of funcToMock', () => {
  funcToMock.mockImplementation(() => { /* implementation specific to this test */ });
  // (funcToMock as jest.Mock)... in TS

  // ...
});

More Related Contents:

  1. How to mock functions in the same module using Jest?
  2. How can I mock an ES6 module import using Jest?
  3. How do I test axios in Jest?
  4. Jest mock inner function
  5. How can I mock the JavaScript window object using Jest?
  6. Jest: Timer and Promise don’t work well. (setTimeout and async function)
  7. Mocking globals in Jest
  8. Jest: How to mock one specific method of a class
  9. Can you write async tests that expect toThrow?
  10. Message “Async callback was not invoked within the 5000 ms timeout specified by jest.setTimeout”
  11. How to test the type of a thrown exception in Jest
  12. How can I use Jest to spy on a method call?
  13. How to mock a constructor like new Date()
  14. Simulate a button click in Jest
  15. how to reset module imported between tests
  16. How do I set a mock date in Jest?
  17. jest unexpected token when importing css
  18. What functions should I mock during unit testing
  19. How to mock Axios with Jest?
  20. Jest: how to mock console when it is used by a third-party-library?
  21. How to mock dependencies for unit tests with ES6 Modules
  22. Jest – SyntaxError: Cannot use import statement outside a module
  23. Mock inner axios.create()
  24. Remove logging the origin line in Jest
  25. Mocking dayjs extend
  26. Jest spyOn function called
  27. How to mock React component methods with jest and enzyme
  28. Jest matcher to match any one of three values
  29. Is it possible to put test files under pages directory in Next.js?
  30. XMLHttpRequest testing in Jest

Leave a Comment