public static Map<String, Map<String, Long>> makeStorageMap(int numAccounts, int numContainerPerAccount,
      long maxValue, long minValue) {
    Random random = new Random();
    Map<String, Map<String, Long>> accountMap = new HashMap<>();

    short accountId = 1;
    for (int i = 0; i < numAccounts; i++) {
      Map<String, Long> containerMap = new HashMap<>();
      accountMap.put(String.valueOf(accountId), containerMap);

      short containerId = 1;
      for (int j = 0; j < numContainerPerAccount; j++) {
        long usage = Math.abs(random.nextLong()) % (maxValue - minValue) + minValue;
        containerMap.put(String.valueOf(containerId), usage);
        containerId++;
      }
      accountId++;
    }
    return accountMap;
  }
Create a container storage map. This map will have to levels. First level's key is the account id. Second level's
key is the container id. Account ids and container ids are both ranging from 1. The value would the storage usage,
which will be greater than or equal to {@code minValue} and less than {@code maxValue}.
@param numAccounts The number of accounts in the returned map.
@param numContainerPerAccount The number of container under each account
@param maxValue The maximum value for storage usage.
@param minValue The minimum value for storage usage.
@return A map representing the container storage usage.
ambry-test-utils/src/main/java/com/github/ambry/utils/TestUtils.java