Add TODO

process_results is as of now tested separately because the corresponding
iterator is not exposed nicely, and because it is not `Clone`.

However, the respective tests already diverged. Instead of fixing
process_results, we should strive to uniformly use test_specializations
for ProcessResults, too.

tests/specializations.rs

@@ -129,6 +129,7 @@ quickcheck! {
 }
 
 quickcheck! {
+    // TODO Replace this function by a normal call to test_specializations
     fn process_results(v: Vec<Result<u8, u8>>) -> () {
         helper(v.iter().copied());
         helper(v.iter().copied().filter(Result::is_ok));