NamenodeProtocols nnRpc = nn.getRpcServer();
SecondaryNameNode secondary = startSecondaryNameNode(conf);
// prepare checkpoint image
secondary.doCheckpoint();
CheckpointSignature sig = nnRpc.rollEditLog();
// manipulate the CheckpointSignature fields
sig.setBlockpoolID("somerandomebpid");
sig.clusterID = "somerandomcid";
try {
sig.validateStorageInfo(nn.getFSImage()); // this should fail