### Question:
RecyclerItemAdapter extends RecyclerView.Adapter<ItemViewHolder> implements ItemHierarchy.Observer { public ItemHierarchy getRootItemHierarchy() { return itemHierarchy; } RecyclerItemAdapter(ItemHierarchy hierarchy); IItem getItem(int position); @Override long getItemId(int position); @Override int getItemCount(); @Override ItemViewHolder onCreateViewHolder(ViewGroup parent, int viewType); @Override void onBindViewHolder(ItemViewHolder holder, int position); @Override int getItemViewType(int position); @Override void onChanged(ItemHierarchy hierarchy); @Override void onItemRangeChanged(ItemHierarchy itemHierarchy, int positionStart, int itemCount); @Override void onItemRangeInserted(ItemHierarchy itemHierarchy, int positionStart, int itemCount); @Override void onItemRangeMoved(
      ItemHierarchy itemHierarchy, int fromPosition, int toPosition, int itemCount); @Override void onItemRangeRemoved(ItemHierarchy itemHierarchy, int positionStart, int itemCount); ItemHierarchy findItemById(int id); ItemHierarchy getRootItemHierarchy(); void setOnItemSelectedListener(OnItemSelectedListener listener); static final String TAG_NO_BACKGROUND; }### Answer:
@Test public void testGetRootItemHierarchy() { RecyclerItemAdapter adapter = new RecyclerItemAdapter(mItemGroup); ItemHierarchy root = adapter.getRootItemHierarchy(); assertSame("Root item hierarchy should be mItemGroup", mItemGroup, root); }