public String submitNotebookSolutionAttempt() {
        final boolean isCorrect = notebookProblemSet.verifyNotebook(notebook);
        final StringBuilder resultStringBuilder = new StringBuilder(notebookProblemSet.getMessageFromLastTest());
        if (isCorrect) {
            if (notebookProblemSet.hasNextProblem()) {
                notebookProblemSet.beginNextProblem();
            } else {
                resultStringBuilder.append("You beat the game!");
            }
        }
        return resultStringBuilder.toString();
    }