### Question:
HtmlSeLionElementSet extends SeLionElementSet { public boolean add(String element) { return super.add(new HtmlSeLionElement(element)); } HtmlSeLionElementSet(Collection<SeLionElement> elements); static HtmlSeLionElementSet getInstance(); boolean add(String element); List<GUIObjectDetails> getGUIObjectList(List<String> keys);  }### Answer:
@Test public void testAdd() { SeLionElementSet elementSet = HtmlSeLionElementSet.getInstance(); elementSet.add("com.foo.HtmlSelionElementSetTest"); Optional<SeLionElement> first = elementSet.stream().findFirst(); assertEquals(first.orElse(null).getElementClass(), "HtmlSelionElementSetTest", "the custom added element is not first"); }