* <p>
     * Effective properties are computed from system, user and optionally project properties, layered with
     * defined precedence onto each other to achieve proper precedence. Precedence is defined as:
     * <ul>
     *     <li>System properties (lowest precedence)</li>
     *     <li>Project properties (optional)</li>
     *     <li>User properties (highest precedence)</li>

      // If ApiProxy doesn't exist, we're not on AppEngine at all.
      return false;
    } catch (InvocationTargetException e) {
      // If ApiProxy throws an exception, we're not in a proper AppEngine environment.
      return false;
    } catch (IllegalAccessException e) {
      // If the method isn't accessible, we're not on a supported version of AppEngine;
      return false;

    throw new UnsupportedOperationException();
  }

  /**
   * Not supported. <b>You are attempting to create a set that may contain a non-{@code Comparable}
   * element.</b> Proper calls will resolve to the version in {@code ImmutableSortedSet}, not this
   * dummy version.
   *
   * @throws UnsupportedOperationException always

 * thrown away immediately once repository system was created and there is no need for more instances. If new
 * repository system instance needed, new instance of this class must be created. For proper shut down of returned
 * repository system instance(s) use {@link RepositorySystem#shutdown()} method on supplied instance(s).
 * <p>

    throw new UnsupportedOperationException();
  }

  /**
   * Not supported. <b>You are attempting to create a multiset that may contain a non-{@code
   * Comparable} element.</b> Proper calls will resolve to the version in {@code
   * ImmutableSortedMultiset}, not this dummy version.
   *
   * @throws UnsupportedOperationException always

        assertFalse(DefaultMirrorSelector.isExternalRepo(getRepo("foo", "file:///somepath")));
        assertFalse(DefaultMirrorSelector.isExternalRepo(getRepo("foo", "file://D:/somepath")));

        // not a proper url so returns false;
        assertFalse(DefaultMirrorSelector.isExternalRepo(getRepo("foo", "192.168.101.1")));
        assertFalse(DefaultMirrorSelector.isExternalRepo(getRepo("foo", "")));
    }

    @Test

  /**
   * The HTTP <a href="https://goo.gl/VKpXxa">{@code X-Download-Options}</a> header field name.
   *
   * <p>When the new X-Download-Options header is present with the value {@code noopen}, the user is
   * prevented from opening a file download directly; instead, they must first save the file
   * locally.
   *
   * @since 24.1
   */

                PlexusConfiguration config = XmlPlexusConfiguration.toPlexusConfiguration(dom);
                configProps.put("aether.transport.wagon.config." + server.getId(), config);

                // Translate to proper resolver configuration properties as well (as Plexus XML above is Wagon specific
                // only) but support only configuration/httpConfiguration/all, see