### Question:
MasterContainer extends BaseWidget implements ComponentContainer { public RegistrationEntry register(final Window window) { this.window.add(window); requestRepaint(); return new RegistrationEntry() { @Override public void unregister() { MasterContainer.this.window.remove(window); requestRepaint(); } @Override public boolean isRegistered() { return MasterContainer.this.window.contains(window); } }; } MasterContainer(); Iterator<NonUIComponent> getNonUIComponentIterator(); void addNonUIComponent(NonUIComponent component); void removeNonUIComponent(NonUIComponent component); void addDataSource(DataSource dataSource); Canvas getPane(); void setPane(Canvas pane); SC getSC(); RegistrationEntry register(final Window window); @Override void paintContent(PaintTarget target); @Override void addComponent(Component c); @Override void removeComponent(Component c); @Override void removeAllComponents(); @Override void replaceComponent(Component oldComponent, Component newComponent); @Override Iterator<Component> getComponentIterator(); @Override void requestRepaintAll(); @Override void moveComponentsFrom(ComponentContainer source); @Override void addListener(ComponentAttachListener listener); @Override void removeListener(ComponentAttachListener listener); @Override void addListener(ComponentDetachListener listener); @Override void removeListener(ComponentDetachListener listener);  }### Answer:
@Test public void test_registerWindow() { final Window window = mock(Window.class); assertTrue(container.register(window).isRegistered()); }
@Test public void test_unregisterWindow() { final Window window = mock(Window.class); final RegistrationEntry registration = container.register(window); registration.unregister(); assertFalse(registration.isRegistered()); }