Function assertPrevButtonScrolling

src/material/tabs/tab-header.spec.ts:535–568

* Asserts that auto scrolling using the previous 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 assertPrevButtonScrolling(startEventName: string, endEventName: string) {
        header.scrollDistance = Infinity;
        fixture.detectChanges();

        let currentScroll = header.scrollDistance;

        expect(currentScroll).withContext('Expected to start off scrolled.').toBeGreaterThan(0);

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

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

        // Wait to exceed delay (300 + 500 = 800ms > 650ms)
        await wait(600);

        expect(header.scrollDistance)
          .withContext('Expected to scroll after some time.')
          .toBeLessThan(currentScroll);

        currentScroll = header.scrollDistance;
        await wait(200);

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

        dispatchFakeEvent(nextButton, endEventName);
        // Wait for any cleanup or final events
        await wait(100);
      }
    });

    describe('disabling pagination', () => {