@Test
  public void testWALCoprocessorLoaded() throws Exception {
    // test to see whether the coprocessor is loaded or not.
    WALCoprocessorHost host = wals.getWAL(null).getCoprocessorHost();
    Coprocessor c = host.findCoprocessor(SampleRegionWALCoprocessor.class);
    assertNotNull(c);
  }
A loaded WAL coprocessor won't break existing WAL test cases.
hbase-server/src/test/java/org/apache/hadoop/hbase/wal/TestWALFactory.java