private SequentialExecutor e;

  @Override
  public void setUp() {
    fakePool = new FakeExecutor();
    e = new SequentialExecutor(fakePool);
  }

  public void testConstructingWithNullExecutor_fails() {
    assertThrows(NullPointerException.class, () -> new SequentialExecutor(null));
  }

  public void testBasics() {
    AtomicInteger totalCalls = new AtomicInteger();
    Runnable intCounter =