@Override
        protected Writer createWriter(Path logfile) throws IOException {
          Writer mockWriter = Mockito.mock(Writer.class);
          Mockito.doThrow(new IOException("Injected")).when(mockWriter)
            .append(Mockito.<Entry> any());
          return mockWriter;
        }
@return set of wal names present prior to split attempt.
@throws IOException if the split process fails
hbase-server/src/test/java/org/apache/hadoop/hbase/wal/TestWALSplit.java