code: private String buildValidationErrorMessage(String message, Object expectedValue, Object actualValue) {
          return message + ", expected '" + expectedValue + "' but was '" + actualValue + "'";
      }
docs: Constructs proper error message with expected value and actual value.
  @param message the base error message.
  @param expectedValue the expected value.
  @param actualValue the actual value.
  @return