How do you cast a List of supertypes to a List of subtypes?

Question

For example, lets say you have two classes:

public class TestA {}
public class TestB extends TestA{}

I have a method that returns a L

Answer 1

Quite strange that manually casting a list is still not provided by some tool box implementing something like:

@SuppressWarnings({ "unchecked", "rawtypes" })
public static  List cast(List list) {
    return (List) list;
}

Of course, this won't check items one by one, but that is precisely what we want to avoid here, if we well know that our implementation only provides the sub-type.