allRenderObjects property
Render objects of all the widgets currently in the widget tree (lazy pre-order traversal).
This will almost certainly include many duplicates since the render object of a StatelessWidget or StatefulWidget is the render object of its child; only RenderObjectWidgets have their own render object.
Implementation
Iterable<RenderObject> get allRenderObjects {
TestAsyncUtils.guardSync();
return allElements.map<RenderObject>((Element element) => element.renderObject!);
}