@After
  public void after() {
    accountStatsMySqlStore.shutdown();
  }
Integration test for {@link MySqlStorageUsageRefresher}.
It's also the unit test. The reason to have unit test here is we can only be sure mysql server is running
in integration test.
ambry-quota/src/integration-test/java/com/github/ambry/quota/storage/MySqlStorageUsageRefresherTest.java