private SampleRegionWALCoprocessor getCoprocessor(WAL wal,
    Class<? extends SampleRegionWALCoprocessor> clazz) throws Exception {
    WALCoprocessorHost host = wal.getCoprocessorHost();
    Coprocessor c = host.findCoprocessor(clazz.getName());
    return (SampleRegionWALCoprocessor) c;
  }
Test to see CP loaded successfully or not. There is a duplication at TestHLog, but the purpose
of that one is to see whether the loaded CP will impact existing WAL tests or not.
hbase-server/src/test/java/org/apache/hadoop/hbase/coprocessor/TestWALObserver.java