/ #JavaScript #Testing 

Mocking the current Date in Jest tests

There are situations where Date.now is used in application code. That code needs to be tested, and it’s always a struggle to remember how to mock Date.now. Here is the magic snippet:

const literallyJustDateNow = () => Date.now();

test('It should call and return Date.now()', () => {
  const realDateNow = Date.now.bind(global.Date);
  const dateNowStub = jest.fn(() => 1530518207007);
  global.Date.now = dateNowStub;


  global.Date.now = realDateNow;

This was sent out on the Code with Hugo newsletter last Monday. Subscribe to get the latest posts right in your inbox (before anyone else).

This isn’t really a Jest-specific trick, we’re just accessing Node global object and replace Date.now with a stub. We’re also being good unit-testing citizens and putting the original global.Date.now implementation back 😇.

unsplash-logoBryce Barker


Hugo Di Francesco

A developer, working out of London writing CSS, JavaScript and Python.

Subscribe to the Code with Hugo newsletter

Get the latest articles in your inbox every 2 weeks