React Unit Testing Example 17

LoadingIndicator.test.js

  describe('on unmount', () => {
    it('should clear timeout', () => {
      jest.useFakeTimers();

      const mockTimerValue = 12345;
      setTimeout.mockReturnValue(mockTimerValue);

      const wrapper = mount(
        <LoadingIndicator isLoading={true}>
          <div>ahoy!</div>
        </LoadingIndicator>
      );

      wrapper.unmount();
      expect(clearTimeout.mock.calls.length).toEqual(1);
      expect(clearTimeout.mock.calls[0][0]).toEqual(mockTimerValue);
    });
  });