@Before
  public void before() throws Exception {
    accountStatsMySqlStore.cleanupTables();
  }
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