@AfterClass
  public static void tearDownAfterClass() throws Exception {
    TEST_UTIL.shutdownMiniCluster();
  }
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