public Collection<PlanCoordinator> coordinators() {
    return Collections.unmodifiableCollection(mCoordinators.values());
  }
@Test
  public void testAddJobUpToCapacity() throws Exception {
    assertEquals("tracker should be empty", 0, mTracker.coordinators().size());
    fillJobTracker(CAPACITY);
    mException.expect(ResourceExhaustedException.class);
    addJob(100);
  }