### Question:
MultiPageGui implements GUI { @Override public void addButton(InventoryItem inventoryItem, Executable executable) { this.addItem(inventoryItem); this.slotActions.addSlotAction(inventoryItem, executable); }  @Override void displayTo(Player player); @Override void clear(); @Override void addButton(InventoryItem inventoryItem, Executable executable); @Override void addItem(InventoryItem item); @Override void removeItem(int slot, int page);  }### Answer:
@Test public void addButton() { when(inventoryPages.getPage(anyInt())).thenReturn(mock(Inventory.class)); MultiPageGui multiPageGui = new MultiPageGui(mock(PlayerPages.class), inventoryPages, slotActions, mock(Server.class), playerPageRearranger); InventoryItem inventoryItem = mock(InventoryItem.class); multiPageGui.addButton(inventoryItem, mock(Executable.class)); verify(slotActions).addSlotAction(eq(inventoryItem), any()); }