public void testStop_alreadyStopped() {
    stopwatch.start();
    stopwatch.stop();
    assertThrows(IllegalStateException.class, stopwatch::stop);
    assertFalse(stopwatch.isRunning());
  }

  public void testReset_new() {
    ticker.advance(1);
    stopwatch.reset();
    assertFalse(stopwatch.isRunning());
    ticker.advance(2);
    assertEquals(0, stopwatch.elapsed(NANOSECONDS));
    stopwatch.start();
    ticker.advance(3);