public Collection<PlanCoordinator> coordinators() {
    return Collections.unmodifiableCollection(mCoordinators.values());
  }
@Test
  public void testPurgeCount() throws Exception {
    PlanTracker tracker = new PlanTracker(10, 0, 5, mMockWorkflowTracker);
    assertEquals("tracker should be empty", 0, tracker.coordinators().size());
    fillJobTracker(tracker, 10);
    finishAllJobs(tracker);
    addJob(tracker, 100);
    assertEquals(6, tracker.coordinators().size());
  }