### Question:
TokenCache { public static void cleanUpTokenReferral(Configuration conf) { conf.unset(MRJobConfig.MAPREDUCE_JOB_CREDENTIALS_BINARY); }  static byte[] getSecretKey(Credentials credentials, Text alias); static void obtainTokensForNamenodes(Credentials credentials,
      Path[] ps, Configuration conf); static void cleanUpTokenReferral(Configuration conf); @InterfaceAudience.Private static Credentials loadTokens(String jobTokenFile, JobConf conf); @InterfaceAudience.Private static void setJobToken(Token<? extends TokenIdentifier> t, 
      Credentials credentials); @SuppressWarnings("unchecked") @InterfaceAudience.Private static Token<JobTokenIdentifier> getJobToken(Credentials credentials); @InterfaceAudience.Private
  static final String JOB_TOKEN_HDFS_FILE; @InterfaceAudience.Private
  static final String JOB_TOKENS_FILENAME; }### Answer:
@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)); }