@Override
    public void postWALWrite(ObserverContext<? extends WALCoprocessorEnvironment> ctx,
      RegionInfo info, WALKey logKey, WALEdit logEdit) throws IOException {
      if (info.getTable().equals(TableName.valueOf("testCPMutationsAreWrittenToWALEdit"))) {
        savedEdit = logEdit;
      }
    }
Tests that added mutations from coprocessors end up in the WAL.
hbase-server/src/test/java/org/apache/hadoop/hbase/coprocessor/TestRegionObserverForAddingMutationsFromCoprocessors.java