### Question:
MRApps extends Apps { public static String toString(JobId jid) { return jid.toString(); } if(userClassesTakesPrecedence); static String toString(JobId jid); static JobId toJobID(String jid); static String toString(TaskId tid); static TaskId toTaskID(String tid); static String toString(TaskAttemptId taid); static TaskAttemptId toTaskAttemptID(String taid); static String taskSymbol(TaskType type); static TaskType taskType(String symbol); static TaskAttemptStateUI taskAttemptState(String attemptStateStr); @SuppressWarnings("deprecation") static void setClasspath(Map<String, String> environment,
      Configuration conf);  }### Answer:
@Test public void testJobIDtoString() { JobId jid = RecordFactoryProvider.getRecordFactory(null).newRecordInstance(JobId.class); jid.setAppId(RecordFactoryProvider.getRecordFactory(null).newRecordInstance(ApplicationId.class)); assertEquals("job_0_0000", MRApps.toString(jid)); }
@Test public void testTaskIDtoString() { TaskId tid = RecordFactoryProvider.getRecordFactory(null).newRecordInstance(TaskId.class); tid.setJobId(RecordFactoryProvider.getRecordFactory(null).newRecordInstance(JobId.class)); tid.getJobId().setAppId(RecordFactoryProvider.getRecordFactory(null).newRecordInstance(ApplicationId.class)); tid.setTaskType(TaskType.MAP); TaskType type = tid.getTaskType(); System.err.println(type); type = TaskType.REDUCE; System.err.println(type); System.err.println(tid.getTaskType()); assertEquals("task_0_0000_m_000000", MRApps.toString(tid)); tid.setTaskType(TaskType.REDUCE); assertEquals("task_0_0000_r_000000", MRApps.toString(tid)); }
@Test public void testTaskAttemptIDtoString() { TaskAttemptId taid = RecordFactoryProvider.getRecordFactory(null).newRecordInstance(TaskAttemptId.class); taid.setTaskId(RecordFactoryProvider.getRecordFactory(null).newRecordInstance(TaskId.class)); taid.getTaskId().setTaskType(TaskType.MAP); taid.getTaskId().setJobId(RecordFactoryProvider.getRecordFactory(null).newRecordInstance(JobId.class)); taid.getTaskId().getJobId().setAppId(RecordFactoryProvider.getRecordFactory(null).newRecordInstance(ApplicationId.class)); assertEquals("attempt_0_0000_m_000000_0", MRApps.toString(taid)); }