### Question:
OverlayView implements ExpandedView.ExpandedViewCallback { void showExpandedView(Activity activity, List<Page> pages, Page selected, boolean animated) { expandedView.displayPages(pages, selected, animated); activity.getWindowManager().addView(expandedView, wrap(EXPANDED_VIEW_PARAMS)); } OverlayView(Context context, DragHelper dragHelper, ExpandedView expandedView); @Override void finish(); @Nullable @Override View findViewById(int id); @Override void onPageSelected(Page page);  }### Answer:
@Test public void showExpandedView() { final List<Page> pages = IntStream.range(0, 5).mapToObj(this::createPage).collect(Collectors.toList()); view.showExpandedView(activity, pages, pages.get(1), false); verify(windowManager).addView(eq(expandedView), any()); verify(expandedView).displayPages(eq(pages), eq(pages.get(1)), eq(false)); }