public static void cleanUpTokenReferral(Configuration conf) {
    conf.unset(MRJobConfig.MAPREDUCE_JOB_CREDENTIALS_BINARY);
  }
@Test
  public void testCleanUpTokenReferral() throws Exception {
    Configuration conf = new Configuration();
    conf.set(MRJobConfig.MAPREDUCE_JOB_CREDENTIALS_BINARY, "foo");
    TokenCache.cleanUpTokenReferral(conf);
    assertNull(conf.get(MRJobConfig.MAPREDUCE_JOB_CREDENTIALS_BINARY));
  }