String xml = "<extension></extension>";

        ExtensionDescriptor ed = builder.build(toStream(xml));

        assertNotNull(ed);
        assertNotNull(ed.getExportedPackages());
        assertTrue(ed.getExportedPackages().isEmpty());
        assertNotNull(ed.getExportedArtifacts());
        assertTrue(ed.getExportedArtifacts().isEmpty());
    }

    @Test
    void testCompleteDescriptor() throws Exception {

     */
    public Set<String> getExportedArtifacts() {
        return artifacts;
    }

    /**
     * Returns classpath elements exported by the extension.
     */
    public Set<String> getExportedPackages() {
        return packages;
    }

    /**
     * The key that can be used to identify the configuration using the
     * {@link javax.inject.Named} annotation.
     */
    public String getKey() {

            CoreExtensionEntry coreEntry, List<CoreExtensionEntry> extensionEntries) {
        Set<String> exportedPackages = new HashSet<>(coreEntry.getExportedPackages());
        for (CoreExtensionEntry extension : extensionEntries) {
            exportedPackages.addAll(extension.getExportedPackages());
        }
        return exportedPackages;
    }

    /**

    private final Set<String> artifacts;

    private final Map<String, ClassLoader> packages;

    public CoreExports(CoreExtensionEntry entry) {
        this(entry.getClassRealm(), entry.getExportedArtifacts(), entry.getExportedPackages());
    }

    public CoreExports(ClassRealm realm, Set<String> exportedArtifacts, Set<String> exportedPackages) {
        this.artifacts = Collections.unmodifiableSet(new HashSet<>(exportedArtifacts));

    private List<String> exportedPackages;

    private List<String> exportedArtifacts;

    ExtensionDescriptor() {
        // hide constructor
    }

    public List<String> getExportedPackages() {
        if (exportedPackages == null) {
            exportedPackages = new ArrayList<>();
        }

        return exportedPackages;
    }

            extensionRealms.add(extensionRealm);
            if (extensionDescriptor != null) {
                exportedPackages.put(extensionRealm, extensionDescriptor.getExportedPackages());
                exportedArtifacts.put(extensionRealm, extensionDescriptor.getExportedArtifacts());
            }

            if (!plugin.isExtensions()
                    && artifacts.size() == 1

        if (STRATEGY_PARENT_FIRST.equals(classLoadingStrategy)) {
            realm.importFrom(parentRealm, "");
        } else if (STRATEGY_PLUGIN.equals(classLoadingStrategy)) {
            coreExports.getExportedPackages().forEach((p, cl) -> realm.importFrom(cl, p));
            providedArtifacts = coreExports.getExportedArtifacts();
        } else if (STRATEGY_SELF_FIRST.equals(classLoadingStrategy)) {

        if (STRATEGY_PARENT_FIRST.equals(classLoadingStrategy)) {
            realm.importFrom(parentRealm, "");
        } else if (STRATEGY_PLUGIN.equals(classLoadingStrategy)) {
            coreExports.getExportedPackages().forEach((p, cl) -> realm.importFrom(cl, p));
            providedArtifacts = coreExports.getExportedArtifacts();
        } else if (STRATEGY_SELF_FIRST.equals(classLoadingStrategy)) {

        this.world = coreRealm.getClassWorld();
        this.containerRealm = coreRealm.getRealm();
        this.delegates = delegates;

        Map<String, ClassLoader> foreignImports = exports.getExportedPackages();

        this.mavenApiRealm = createRealm(
                API_REALMID,
                RealmType.Core,
                null /* parent */,
                null /* parentImports */,

        Set<String> exportedPackages = new HashSet<>(coreEntry.getExportedPackages());
        for (CoreExtensionEntry extension : extensions) {
            exportedArtifacts.addAll(extension.getExportedArtifacts());
            exportedPackages.addAll(extension.getExportedPackages());
        }