### Question:
SimpleButtonMenuVM implements ButtonMenuVM { @Override public Set<ButtonVM> getButtonVMs() { return buttonVMs; } SimpleButtonMenuVM();  SimpleButtonMenuVM(ButtonVM buttonVM);  SimpleButtonMenuVM(Collection<ButtonVM> buttons); @Override Set<ButtonVM> getButtonVMs(); @Override void enable(); @Override void disable(); void addItem(final ButtonVM buttonVM); void removeItem(final ButtonVM buttonVM); @Override void registerListener(ButtonMenuVMListener listener); @Override void unregisterListener(ButtonMenuVMListener listener);  }### Answer:
@Test public void shouldBeEmptyAfterConstruction() { assertTrue(simpleButtonMenuVM.getButtonVMs().isEmpty()); }