New matcher: .toHaveBeenCalledBefore(mock)

[mattphillips]

Feature Request

.toHaveBeenCalledBefore(mock)

Use .toHaveBeenCalledBefore when checking if a mock has been called before another mock.

it('calls mock1 before mock2', () => {
  const mock1 = jest.fn();
  const mock2 = jest.fn();

  mock1();
  mock2();
  mock1();

  expect(mock1).toHaveBeenCalledBefore(mock2);
});

[mattphillips]

taken from jestjs/jest#4402

[mattphillips]

Blocked pending internal timestamp support in Jest: jestjs/jest#4866

[tejasbubane]

I would like to work on this. Will keep an eye on the pending Jest issue.

[tejasbubane]

The PR is merged, should I wait for next release of jest?

[mattphillips]

@tejasbubane you could work on it now but we will have to sync merging/releasing this matcher with the next release of Jest.

We should also probably add a note to the matcher docs that it will only be compatible with >jest@22

[ChrisCinelli]

I am getting:

    TypeError: expect(...).toHaveBeenCalledBefore is not a function

I am using [email protected] and [email protected]

[mattphillips]

Hey @ChrisCinelli this matcher hasn’t been implemented yet.

@tejasbubane jest@22 has landed now do you still want to work on this? If not I can look into getting it added tomorrow 😄

[ChrisCinelli]

Yes, I found out.

But I have bad news:

        console.log(setup.mock.timestamps);
        console.log(middleware.mock.timestamps);

Yield to:

  console.log lib/middleware.spec.js:12
    [ 1515112206835 ]

  console.log lib/middleware.spec.js:13
    [ 1515112206835 ]

[ChrisCinelli]

To implement .toHaveBeenCalledBefore we may need a global counter incremented at every call to an instance of a jest.fn() and saving the current value in something likemyFunc.mock.callOrder (or jasmine call it invocationOrder). But this will require another change in Jest.

[mattphillips]

@tejasbubane @ChrisCinelli I've added and published this matcher in v0.6.0 so I'm going to close this issue.

@ChrisCinelli because of the calls to mocks happening in the same event loop the timestamps are identical - as you described. Because of this for this matcher to work it depends on the mock being asynchronous and ran in a different context. For example:

const timeout = time => () => new Promise(res => setTimeout(() => res()), time);

it('calls mock1 before mock2', async () => {
  const mock1 = jest.fn(timeout(1));
  const mock2 = jest.fn(timeout(1));

  await mock1();
  await mock2();
  await mock1();

  expect(mock1).toHaveBeenCalledBefore(mock2);
});

[benjamin21st]

Wouldn't it be more scalable to implement an API for .series as opposed to limiting one is called before another?

What if use cases come up for three calls? 1000?

[mattphillips]

Hey @benjamin21st feel free to open a new issue and propose the API that you think would be more scalable 😄