code: public static <T1, T2> BiPredicate<T1, T2> spyRes(BiPredicate<T1, T2> predicate, Box<Boolean> result) {
          return spy(predicate, result, Box.<T1>empty(), Box.<T2>empty());
      }
docs: Proxies a binary predicate spying for result.
  
  @param <T1> the predicate first parameter type
  @param <T2> the predicate second parameter type
  @param predicate the predicate that will be spied
  @param result a box that will be containing spied result
  @return the proxied predicate