code: private void failWithMessage(String errorMessage) {
        AssertionError assertionError = Failures.instance().failureIfErrorMessageIsOverridden(info);
        if (assertionError == null) {
          // error message was not overridden, build it.
          String description = MessageFormatter.instance().format(info.description(), info.representation(), "");
          assertionError = new AssertionError(description + errorMessage);
        }
        Failures.instance().removeAssertJRelatedElementsFromStackTraceIfNeeded(assertionError);
        throw assertionError;
      }
docs: Copy from AssertJ to prevent errors with percents in error message