}
    }

    @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);

        // 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<>();

            // 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) {

    }

    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"));
            }
        }