Sub class algorithm - one for all solution

[ryucc]

Intro

We want to mock this method

List<Integer> getList() {
   return new MyListImpl();
}

The most ideal target would be subclassing MyListImpl.

This might not be possible if MyListImpl is final. What is our next choice?

Previously, we did a DFS on MyListImpl, on the inheritance graph from MyListImpl to List, and use the closest class on the path to List.

But we can actually make a new class that implements every parent class of MyListImpl. This will have better robustness to class casting.