Function assertNextButtonScrolling

src/material/tabs/tab-header.spec.ts:500–528

* Asserts that auto scrolling using the next button works. * @param startEventName Name of the event that is supposed to start the scrolling. * @param endEventName Name of the event that is supposed to end the scrolling.

(startEventName: string, endEventName: string)

       * @param endEventName Name of the event that is supposed to end the scrolling.
       */
      async function assertNextButtonScrolling(startEventName: string, endEventName: string) {
        expect(header.scrollDistance).withContext('Expected to start off not scrolled.').toBe(0);

        dispatchFakeEvent(nextButton, startEventName);
        fixture.detectChanges();
        await wait(300);

        expect(header.scrollDistance)
          .withContext('Expected not to scroll after short amount of time.')
          .toBe(0);

        await wait(600);

        expect(header.scrollDistance)
          .withContext('Expected to scroll after some time.')
          .toBeGreaterThan(0);

        let previousDistance = header.scrollDistance;

        // Wait for interval (100ms)
        await wait(200);

        expect(header.scrollDistance)
          .withContext('Expected to scroll again after some more time.')
          .toBeGreaterThan(previousDistance);

        dispatchFakeEvent(nextButton, endEventName);
        await wait(100);
      }

      /**
       * Asserts that auto scrolling using the previous button works.