results.add(result2);

        ProjectBuildingException exception = new ProjectBuildingException(results);
        String message = exception.getMessage();

        assertTrue(
                message.contains("3 problems were encountered while processing the POMs (2 errors)"),
                "Message should contain problem count and error count");

     *
     * @param severity the severity level to get problems for
     * @return a stream of problems with the specified severity
     */
    @Nonnull
    Stream<P> problems(BuilderProblem.Severity severity);

    /**
     * Creates an "empty" problem collector that doesn't store any problems.
     *
     * @param <P> the type of problem
     * @return an empty problem collector
     */
    @Nonnull

     * @param problems the collection of problems to include in the message
     * @return a formatted message including details of all problems
     */
    protected static String buildMessage(String message, ProblemCollector<BuilderProblem> problems) {
        StringBuilder msg = new StringBuilder(message);
        problems.problems().forEach(problem -> msg.append("\n * ")
                .append(problem.getSeverity().name())

     */
    public static <T> Result<T> newResult(T model, Iterable<? extends ModelProblem> problems) {
        return new Result<>(hasErrors(problems), model, problems);
    }

    /**
     * New result consisting of given result and new problem. Convenience for newResult(result.get(),
     * concat(result.getProblems(),problems)).
     *
     * @param result
     * @param problem
     */

        return null;
    }

    static String toMessage(String modelId, List<ModelProblem> problems) {
        StringWriter buffer = new StringWriter(1024);

        PrintWriter writer = new PrintWriter(buffer);

        writer.print(problems.size());
        writer.print((problems.size() == 1) ? " problem was " : " problems were ");
        writer.print("encountered while building the effective model");

        }

        if (hasErrors(problems.getProblems())) {
            throw new SettingsBuildingException(problems.getProblems());
        }

        return new DefaultSettingsBuildingResult(userSettings, problems.getProblems());
    }

    private boolean hasErrors(List<SettingsProblem> problems) {
        if (problems != null) {
            for (SettingsProblem problem : problems) {

        collector.add(Problem.Severity.ERROR, "Error message", 10, 5, null);
        collector.add(Problem.Severity.WARNING, "Warning message", 15, 3, null);

        List<Problem> problems = collector.getProblems();
        assertEquals(2, problems.size(), "Should collect both problems");
        assertEquals(Problem.Severity.ERROR, problems.get(0).getSeverity(), "First problem should be ERROR");

                validateStringNotEmpty(problems, "mirrors.mirror.id", mirror.getId(), mirror.getUrl());

                validateBannedCharacters(
                        problems, "mirrors.mirror.id", Severity.WARNING, mirror.getId(), null, ILLEGAL_REPO_ID_CHARS);

                if ("local".equals(mirror.getId())) {
                    addViolation(
                            problems,
                            Severity.WARNING,

    private final List<SettingsProblem> problems;

    /**
     * Creates a new exception with the specified problems.
     *
     * @param problems The problems that cause this exception, may be {@code null}.
     */
    public SettingsBuildingException(List<SettingsProblem> problems) {
        super(toMessage(problems));

        this.problems = new ArrayList<>();
        if (problems != null) {

        repo.setUrl("http://xxx.xxx.com");
        problems = new SimpleProblemCollector();
        validator.validate(model, problems);
        assertEquals(1, problems.messages.size());

        repo.setId("xxx");
        problems = new SimpleProblemCollector();
        validator.validate(model, problems);
        assertEquals(0, problems.messages.size());
    }

    @Test
    void testValidateMirror() throws Exception {