### Question:
CapacityScheduler extends
    AbstractYarnScheduler<FiCaSchedulerApp, FiCaSchedulerNode> implements
    PreemptableResourceScheduler, CapacitySchedulerContext, Configurable { @Override public Comparator<FiCaSchedulerApp> getApplicationComparator() { return applicationComparator; } CapacityScheduler(); @Override void setConf(Configuration conf); @Override Configuration getConf(); @VisibleForTesting synchronized String getMappedQueueForTest(String user); @Override QueueMetrics getRootQueueMetrics(); CSQueue getRootQueue(); @Override CapacitySchedulerConfiguration getConfiguration(); @Override synchronized RMContainerTokenSecretManager getContainerTokenSecretManager(); @Override Comparator<FiCaSchedulerApp> getApplicationComparator(); @Override ResourceCalculator getResourceCalculator(); @Override Comparator<CSQueue> getQueueComparator(); @Override int getNumClusterNodes(); @Override synchronized RMContext getRMContext(); @Override synchronized void setRMContext(RMContext rmContext); @Override void serviceInit(Configuration conf); @Override void serviceStart(); @Override void serviceStop(); @Override synchronized void reinitialize(Configuration conf, RMContext rmContext); @VisibleForTesting static void setQueueAcls(YarnAuthorizationProvider authorizer,
      Map<String, CSQueue> queues); CSQueue getQueue(String queueName); @Override @Lock(Lock.NoLock.class) Allocation allocate(ApplicationAttemptId applicationAttemptId,
      List<ResourceRequest> ask, List<ContainerId> release, 
      List<String> blacklistAdditions, List<String> blacklistRemovals); @Override @Lock(Lock.NoLock.class) QueueInfo getQueueInfo(String queueName, 
      boolean includeChildQueues, boolean recursive); @Override @Lock(Lock.NoLock.class) List<QueueUserACLInfo> getQueueUserAclInfo(); @Override void handle(SchedulerEvent event); @Lock(Lock.NoLock.class) @VisibleForTesting @Override FiCaSchedulerApp getApplicationAttempt(
      ApplicationAttemptId applicationAttemptId); @Lock(Lock.NoLock.class) FiCaSchedulerNode getNode(NodeId nodeId); @Override @Lock(Lock.NoLock.class) void recover(RMState state); @Override void dropContainerReservation(RMContainer container); @Override void preemptContainer(ApplicationAttemptId aid, RMContainer cont); @Override void killContainer(RMContainer cont); @Override synchronized boolean checkAccess(UserGroupInformation callerUGI,
      QueueACL acl, String queueName); @Override List<ApplicationAttemptId> getAppsInQueue(String queueName); @Override synchronized void removeQueue(String queueName); @Override synchronized void addQueue(Queue queue); @Override synchronized void setEntitlement(String inQueue,
      QueueEntitlement entitlement); @Override synchronized String moveApplication(ApplicationId appId,
      String targetQueueName); @Override EnumSet<SchedulerResourceTypes> getSchedulingResourceTypes(); @Override Resource getMaximumResourceCapability(String queueName); @Override Set<String> getPlanQueues(); @Private
  static final String ROOT_QUEUE; }### Answer:
@Test (timeout = 5000) public void testApplicationComparator() { CapacityScheduler cs = new CapacityScheduler(); Comparator<FiCaSchedulerApp> appComparator= cs.getApplicationComparator(); ApplicationId id1 = ApplicationId.newInstance(1, 1); ApplicationId id2 = ApplicationId.newInstance(1, 2); ApplicationId id3 = ApplicationId.newInstance(2, 1); FiCaSchedulerApp app1 = Mockito.mock(FiCaSchedulerApp.class); when(app1.getApplicationId()).thenReturn(id1); FiCaSchedulerApp app2 = Mockito.mock(FiCaSchedulerApp.class); when(app2.getApplicationId()).thenReturn(id2); FiCaSchedulerApp app3 = Mockito.mock(FiCaSchedulerApp.class); when(app3.getApplicationId()).thenReturn(id3); assertTrue(appComparator.compare(app1, app2) < 0); assertTrue(appComparator.compare(app1, app3) < 0); assertTrue(appComparator.compare(app2, app3) < 0); }