Feature: allow to assert time intervals with .toHaveBeenCalledTimes

[acostalima]

Do you want to request a feature or report a bug?

Feature

What is the current behavior?

.toHaveBeenCalledTimes could be further enhanced to allow to expect successive calls to the same function to occur in given instants. This feature particularly useful in a scenario where one wants to ensure exponential back-off is working properly.

What is the potential behavior?

.toHaveBeenCalledTimes fails when the specified timing constraints are not fulfilled.

Implementation

Possibly allow to pass in a second (optional) argument to .toHaveBeenCalledTimes that would be an array specifying, in milliseconds, the minimum time between each consecutive call to a mocked function. It should be fairly straight forward to implement this as it should be only necessary to record the timestamp for each call to the mocked function, and then compare the differences between the timestamps with the received array.

[SimenB]

This seems like a perfect fit for a custom matcher. @mattphillips thoughts?

[mattphillips]

Hey @SimenB this could certainly be a custom matcher in jest-extended. It sounds similar in implementation to the toHaveBeenCalledBefore matcher.

We currently have an issue with recording the timestamp of when one or more mocks are invoked (potentially multiple times) during the same tick of the event loop they can arrive at the same timestamp value see.

@acostalima this matcher can however be achieved still with the above issue, you would just have to make sure that the mock is actually asynchronous and await it to get differing timestamps. Do you have an example of how you would like the API to look?

Off the top of my head would it be something like the following?

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

it('calls mock1 twice with no more than 50ms in between invocations', async () => {
  const mock1 = jest.fn(timeout(10));

  await mock1();
  await mock1();

  expect(mock1).toHaveBeenCalledBy([50]);
});

Feel free to open an issue for this in jest-extended with the API you'd like and we can work on getting this available for you 😄

[SimenB]

Closing as per above comment. Thanks @mattphillips!

[acostalima]

@SimenB @mattphillips
Thanks for the quick reply!
The above proposal is looking good. I will open an issue in jest-extended so we can proceed this discussion. 😄

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