### Question:
LienzoPanelFocusHandler { public LienzoPanelFocusHandler listen(final LienzoPanel panel, final Command onFocus, final Command onLostFocus) { clear(); overHandler = panel.getView().addMouseOverHandler(mouseOverEvent -> onFocus.execute()); outHandler = panel.getView().addMouseOutHandler(mouseOutEvent -> onLostFocus.execute()); return this; }  LienzoPanelFocusHandler listen(final LienzoPanel panel,
                                          final Command onFocus,
                                          final Command onLostFocus); LienzoPanelFocusHandler clear();  }### Answer:
@Test public void testListen() { tested.listen(panel, onFocus, onLostFocus); ArgumentCaptor<MouseOverHandler> overHandlerArgumentCaptor = ArgumentCaptor.forClass(MouseOverHandler.class); verify(panelView, times(1)).addMouseOverHandler(overHandlerArgumentCaptor.capture()); overHandlerArgumentCaptor.getValue().onMouseOver(mock(MouseOverEvent.class)); verify(onFocus, times(1)).execute(); ArgumentCaptor<MouseOutHandler> outHandlerArgumentCaptor = ArgumentCaptor.forClass(MouseOutHandler.class); verify(panelView, times(1)).addMouseOutHandler(outHandlerArgumentCaptor.capture()); outHandlerArgumentCaptor.getValue().onMouseOut(mock(MouseOutEvent.class)); verify(onLostFocus, times(1)).execute(); }