}
    }

    @Test
    void testV4Model() {
        assertEquals("4.0.0", new MavenModelVersion().getModelVersion(model));
    }

    @Test
    void testV4ModelVersion() {
        Model m = model.withModelVersion("4.1.0");
        assertEquals("4.0.0", new MavenModelVersion().getModelVersion(m));
    }

    @Test
    void testV4ModelRoot() {
        Model m = model.withRoot(true);

                                : null);
        builder.profiles(prune(model.getProfiles()));

        model = builder.build();
        String modelVersion = new MavenModelVersion().getModelVersion(model);
        if (!ModelBuilder.MODEL_VERSION_4_0_0.equals(modelVersion) && !preserveModelVersion) {
            warnNotDowngraded(project);
        }
        model = model.withModelVersion(modelVersion);

        // Value taken from super model
        // ----------------------------------------------------------------------

        assertEquals("4.0.0", p4.getModelVersion());

        assertEquals("4.0.0", p4.getModelVersion());
    }

        // Top-level elements
        // ----------------------------------------------------------------------

        assertEquals("4.0.0", project.getModelVersion());

        // ----------------------------------------------------------------------
        // Plugins
        // ----------------------------------------------------------------------

        // Value taken from super model
        // ----------------------------------------------------------------------

        assertEquals("4.0.0", project4.getModelVersion());

        Build build = project4.getBuild();
        List<Plugin> plugins = build.getPlugins();

        Map<String, Integer> validPluginCounts = new HashMap<>();

            return new MavenStaxReader().read(is, false, null);
        }
    }

    protected void write(Model model, Path dest) throws IOException, XMLStreamException {
        String version = model.getModelVersion();
        Files.createDirectories(dest.getParent());
        try (Writer w = Files.newBufferedWriter(dest)) {
            MavenStaxWriter writer = new MavenStaxWriter();

            // models without a version starting with 3.4.
            validateStringNotEmpty("modelVersion", problems, Severity.ERROR, Version.V20, m.getModelVersion(), m);

            validateModelVersion(problems, m.getModelVersion(), m, "4.0.0");

            validateStringNoExpression("groupId", problems, Severity.WARNING, Version.V20, m.getGroupId(), m);
            if (parent == null) {

        public void setVersion(String version) {
            this.version = version;
        }

        public Scm getScm() {
            return scm;
        }

        public String getModelVersion() {
            return modelVersion;
        }

        public String getGroupId() {
            return groupId;
        }

        public List<Dependency> getDependencies() {

        final Set<MavenProject> projectsIncludingParents = new HashSet<>();
        for (MavenProject project : session.getProjects()) {
            superPomModels.computeIfAbsent(
                    project.getModelVersion(),
                    v -> superPomProvider.getSuperModel(v).getDelegate());
            boolean isAdded = projectsIncludingParents.add(project);
            MavenProject parent = project.getParent();

    }

    protected void mergeModel_ModelVersion(
            Model target, Model source, boolean sourceDominant, Map<Object, Object> context) {
        String src = source.getModelVersion();
        if (src != null) {
            if (sourceDominant || target.getModelVersion() == null) {
                target.setModelVersion(src);
                target.setLocation("modelVersion", source.getLocation("modelVersion"));
            }
        }