code: @Test public void test_hasExtension_wrapperIsNotExt() throws Exception {
    assertTrue(ExtensionLoader.getExtensionLoader(WrappedExt.class).hasExtension("impl1"));
    assertFalse(ExtensionLoader.getExtensionLoader(WrappedExt.class).hasExtension("impl1,impl2"));
    assertFalse(ExtensionLoader.getExtensionLoader(WrappedExt.class).hasExtension("xxx"));
    assertFalse(ExtensionLoader.getExtensionLoader(WrappedExt.class).hasExtension("wrapper1"));
    try {
      ExtensionLoader.getExtensionLoader(WrappedExt.class).hasExtension(null);
      fail();
    }
   catch (  IllegalArgumentException expected) {
      assertThat(expected.getMessage(),containsString("Extension name == null"));
    }
  }
  