jestSpyOn.js

test('creates Contract on correct date', () => {
  const NOW = '2019-05-03T08:00:00.000Z';
  const mockDateNow = jest
    .spyOn(global.Date, 'now')
    .mockImplementation(() => new Date(NOW).getTime());

  const mutation = `
    mutation createContract {
      createContract {
        startedOn
      }
    }
  `;

  const response = await graphQLRequestAsUser(mutation);
  const { data } = response.body;

  expect(data.startedOn).toEqual(NOW);

  mockDateNow.mockRestore();
});


// or we can use inside beforeEach and afterEach

const now = '2019-05-03T08:00:00.000Z';
let mockDateNow;

beforeEach(() => {
  mockDateNow = jest.spyOn(global.Date, 'now').mockImplementation(() => new Date(now).getTime());
});

afterEach(() => {
  mockDateNow.mockRestore();
});

test('some test name', () => {
  //...do some test stuff here
})

test('another test name', () => {
  //...do some more test stuff here
})