public ProxyExtension extension(String extension) {
        ProxyExtensionWithClassLoader h = extensions.get(extension);
        if (null == h) {
            return null;
        } else {
            return h.getExtension();
        }
    }
@Test
    public void testGetProtocol() {
        assertSame(extension1, extensions.extension(protocol1));
        assertSame(extension2, extensions.extension(protocol2));
        assertNull(extensions.extension(protocol3));
    }