@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));
}