@Test
  public void testWALObserverLoaded() throws Exception {
    WAL log = wals.getWAL(null);
    assertNotNull(getCoprocessor(log, SampleRegionWALCoprocessor.class));
  }
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