SinglePartPanelHelper { public boolean hasNoParts() { return parts.isEmpty(); } SinglePartPanelHelper(Collection<PartDefinition> parts,
                                 PlaceManager placeManager); boolean hasNoParts(); void closeFirstPartAndAddNewOne(Command command);  }
@Test public void thereIsNoPartsTest() { singlePartHelper = new SinglePartPanelHelper(new ArrayList<>(), placeManager); assertTrue(singlePartHelper.hasNoParts()); }