I understand and I agree with Pharo not to implement #sort and #sort: in SequenceableCollection, because it does not make sense for most subclasses. SortedCollection, Heap and Interval are already sorted;
Interval and SortedCollection are only sorted according to one particular sort block, which may not be the default sort block (e.g. for decreasing intervals). For Interval the only sensible solution is #shouldNotImplement, but for SortedCollection it is plausible to make #sort or #sort: change the collection's sort block.
and for LinkedList sorting does not really make sense.
Why not? Unlike arrays you can do linked list mergesort without auxiliary space (though the linked list already has O(n) overhead so that means without extra space compared to what the data structure already needs), and it is still guaranteed O(n log n). Of course I'm not really suggesting to implement LinkedList>>#sort. :-)
So I don't really know what to do to fix the Seaside test. We could ask the Pharo guys to integrate OrderedCollection>>#sort and OrderedCollection>>#sort: into Pharo 1.0, but maybe that's already too late?
Grease-Squeak should provide it. Paolo