@VisibleForTesting
  UUID generatePhoneNumberIdentifierIfNotExists(final String phoneNumber) {
    final UpdateItemResponse response = SET_PNI_TIMER.record(() -> dynamoDbClient.updateItem(UpdateItemRequest.builder()
        .tableName(tableName)
        .key(Map.of(KEY_E164, AttributeValues.fromString(phoneNumber)))
        .updateExpression("SET #pni = if_not_exists(#pni, :pni)")
        .expressionAttributeNames(Map.of("#pni", ATTR_PHONE_NUMBER_IDENTIFIER))
        .expressionAttributeValues(Map.of(":pni", AttributeValues.fromUUID(UUID.randomUUID())))
        .returnValues(ReturnValue.ALL_NEW)
        .build()));

    return AttributeValues.getUUID(response.attributes(), ATTR_PHONE_NUMBER_IDENTIFIER, null);
  }
@Test
  void generatePhoneNumberIdentifierIfNotExists() {
    final String number = "+18005551234";

    assertEquals(phoneNumberIdentifiers.generatePhoneNumberIdentifierIfNotExists(number),
        phoneNumberIdentifiers.generatePhoneNumberIdentifierIfNotExists(number));
  }