Test delay from redux-saga

Background

I have a “gradual-backoff” built into a saga using Redux-saga’s delay() effect.

I am using expectSaga to write the test.

But in order to get the test to work I had to disable the delay.

Question

What is the best way to test the delay amount?

Code

“Back off” function that returns 1s, 2s, or 3s

const BACK_OFF_SERIES = [1000, 2000, 3000];
const backOff = attempt =>
  BACK_OFF_SERIES[Math.min(attempt, BACK_OFF_SERIES.length - 1)];

tryDownload saga

const MAX_ATTEMPTS = 3;
function* tryDownloadFiles(assets, downloadOptions) {
  for (let attempts = MAX_ATTEMPTS; attempts; attempts -= 1) {
    try {
      const urls = yield call(downloader, assets, downloadOptions);
      return urls;
    } catch (error) {
      if (attempts > 1) {
        yield call(delay, backOff(attempts));
      } else {
        yield put(
          showError({
            error: `${error}. Failed!`,
          })
        );
      }
    }
  }
}

And an expectSaga test that uses a provider bypass the delay:

const res = expectSaga(tryDownloadFiles, mockAssets, mockDownloadOptions)
  .provide([
    [matchers.call.fn(delay), null],
    [matchers.call.fn(downloader), throwError(mockError)],
  ])
  // .call(delay, backOff(3))
  // .call(delay, backOff(2))
  // .call(delay, backOff(1))
  .put(showError({ error: `${mockError}. Failed!` }))
  .run();

[ttcg]

This is how I did it. I have to check whether the name of the Function is ‘delayP’ or not. Otherwise, it mocks every calls in my *Saga() method.

Fake const provideDelay = ({ fn }, next) => (fn.name === 'delayP') ? null : next();

Usage to Test addWorkoutSaga

it('should call addWorkoutSaga function', () => {
        return expectSaga(addWorkoutSaga, fakeWorkoutPayload)
            .provide([
                { call: provideDelay },
                [matchers.call.fn(WorkoutService.add), null],
                [matchers.call.fn(fetchWorkoutsSaga), null]
            ])
            .call(WorkoutService.add, fakeWorkoutPayload.payload)
            .put(addWorkout.success())
            .call(fetchWorkoutsSaga)
            .run();
    });

addWorkoutSaga

export function* addWorkoutSaga({ payload }) {
    try {
        yield put(beginAjaxCall());

        // throw error intentionally for calories lower than 50
        if (payload.calories < 50)
            payload.calories = '';

        yield delay(1000);
        yield call(WorkoutService.add, payload);

        yield call(toast.success, "Item added successfully.");
        yield put(closeModal(Modal.AddWorkout));
        yield put(addWorkout.success());
        yield call(fetchWorkoutsSaga);
    }
    catch (error) {
        yield put(addWorkout.failure({ errorMessage: error.statusText }));
        yield call(toast.error, "Error occured.  Please try again.");
    }
}

[cobarx]

I’m trying to do something similar and am not sure how to simulate a delay in 4.0.0-beta2. In redux-saga 1.0.x, you can no longer use the yield call(delay, ms) approach and must call yield delay(ms) directly.

Any suggestions?