@Test
  public void testInitEmptyStorageUsage() {
    JSONStringStorageQuotaSource quotaSource =
        new JSONStringStorageQuotaSource(new HashMap<>(), new InMemAccountService(false, false));
    StorageQuotaEnforcer enforcer = new StorageQuotaEnforcer(config, quotaSource, (StorageUsageRefresher) null);
    enforcer.initStorageUsage(Collections.EMPTY_MAP);
    assertEquals(Collections.EMPTY_MAP, enforcer.getStorageUsages());
  }
Test to initialize the storage usage with empty map.
ambry-quota/src/test/java/com/github/ambry/quota/storage/StorageQuotaEnforcerTest.java