PluginableElementsContainer { public Collection<T> getElements() { return new ArrayList<>(elements.values()); } PluginableElementsContainer();  PluginableElementsContainer(Collection<T> e); Collection<T> getElements(); T getElement(String pluginableId); boolean contains(T element); void addElement(T element); void addListener(PluginableElementEventListener<T> listener); void removeListener(PluginableElementEventListener<T> listener); void removeElement(T element); void changeElement(T element);  }
@Test public void testGetElements() { PluginableClass p = new PluginableClass(); container.addElement(p); Collection<PluginableClass> elements = container.getElements(); AssertJUnit.assertEquals(1, elements.size()); }