public Collection<PlanCoordinator> coordinators() {
    return Collections.unmodifiableCollection(mCoordinators.values());
  }
@Test
  public void testRetentionTime() throws Exception {
    long retentionMs = FormatUtils.parseTimeSize("24h");
    PlanTracker tracker = new PlanTracker(10, retentionMs, -1, mMockWorkflowTracker);
    assertEquals("tracker should be empty", 0, tracker.coordinators().size());
    fillJobTracker(tracker, 10);
    finishAllJobs(tracker);
    mException.expect(ResourceExhaustedException.class);
    addJob(tracker, 100);
  }