public Collection<PlanCoordinator> coordinators() {
    return Collections.unmodifiableCollection(mCoordinators.values());
  }
@Test
  public void testAddJobIncreasesCount() throws Exception {
    assertEquals("tracker should be empty", 0, mTracker.coordinators().size());
    addJob(100);
    assertEquals("tracker should have one job", 1, mTracker.coordinators().size());
  }