### Question:
MouseRequestLifecycle implements CommandRequestLifecycle { void onMouseDown(final @Observes CanvasMouseDownEvent event) { start(); }  void listen(Supplier<CommandRequestLifecycle> target); @Override void start(); @Override void rollback(); @Override void complete(); @PreDestroy void destroy();  }### Answer:
@Test public void testOnMouseDown() { tested.onMouseDown(mock(CanvasMouseDownEvent.class)); verify(lifecycle, times(1)).start(); verify(lifecycle, never()).complete(); verify(lifecycle, never()).rollback(); }