stub a method in abstract parent class

I need to test Class A. I am mocking. How could I stub myMethod() which is a method in the abstract parent class? let's say I have code looking like this :

 public abstract class B<T>
{
 public virtual int myMethod()
   {
   }
}
public class A : class B<T>
{
 //some implementation
 int a = myMethod();
}