@BeforeClass
  public static void setupBeforeClass() throws Exception {
    Configuration conf = TEST_UTIL.getConfiguration();
    conf.setStrings(CoprocessorHost.REGION_COPROCESSOR_CONF_KEY,
      FlushingRegionObserver.class.getName());
    conf.setBoolean(CoprocessorHost.ABORT_ON_ERROR_KEY, true);
    conf.setInt(HConstants.HBASE_CLIENT_RETRIES_NUMBER, 2); // Let's fail fast.
    TEST_UTIL.startMiniCluster(1);
    TEST_UTIL.createTable(TableName.valueOf(tableName), family);
  }
Test that verifies we do not have memstore size negative when a postPut/Delete hook is
slow/expensive and a flush is triggered at the same time the coprocessow is doing its work. To
simulate this we call flush from the coprocessor itself
hbase-server/src/test/java/org/apache/hadoop/hbase/coprocessor/TestNegativeMemStoreSizeWithSlowCoprocessor.java