@Override
    public void preSplitRegionBeforeMETAAction(
      final ObserverContext<MasterCoprocessorEnvironment> ctx, final byte[] splitKey,
      final List<Mutation> metaEntries) throws IOException {
      latch.countDown();
      throw new IOException("Causing rollback of region split");
    }
The below tests are testing split region against a running cluster
hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestSplitTransactionOnCluster.java