public static IReturnsThrows <TMock, TResult> RefCallback <TMock, TResult>(this ICallback <TMock, TResult> mock, Delegate callback)
     where TMock : class
 {
     RefCallbackHelper.SetCallback(mock, callback);
     return((IReturnsThrows <TMock, TResult>)mock);
 }
 public static ICallbackResult RefCallback(this ICallback mock, Delegate callback)
 {
     RefCallbackHelper.SetCallback(mock, callback);
     return((ICallbackResult)mock);
 }