Test runs ok from webstorm, but fails as nx test lib in terminal

Symptoms

The test in question was related to the rxjs code below:

this.allStartTimes$ = this.store.select(selectAllCheckedCountersValues).pipe(
  map(countersValues => {
    const allValues = countersValues
      .map(counterValues => counterValues.values)
      .flat()
      .map(value => value.startTime);

    return sortedUniq(allValues.sort());
  })
);

The tests were failing with generic TypeError , after adding catchError in related observables, the following error was shown:

TypeError: countersValues.map(...).flat is not a function

Which is weird because it is a legit array function and this case runs in from webstorm Run button no prob.

Fix

This is a known issue in ts-jest, adding core-js to test setup fixes the issue, as described here. Weird how it works in webstorm though. In this case, I couldn’t add core-js to test setup, so the workaround was to use flatten from lodash instead of array.flat()

this.allStartTimes$ = this.store.select(selectAllCheckedCountersValues).pipe(
  map(countersValues => {
    const allValues: Value[][] = countersValues.map(
      counterValues => counterValues.values
    );
    const allTimestamps: string[] = flatten(allValues).map(
      (value: Value) => value.startTime
    );

    return sortedUniq(allTimestamps.sort());
  })
);