G'day all.
Quoting Duncan Coutts
On a side note, I've found QuickCheck to be great for these kinds of unit tests. As an example, I was able to turn someone else's code for a trie data structure into a multi-trie (like a bag is to a set) without fully understanding the code and still be fairly confident that the code was correct!
I agree that QuickCheck is great for this kind of task, but I still find myself exporting unnecessary functions. For example, suppose you are writing a balanced binary search tree-based FiniteMap data structure, and want to test it with QuickCheck. As well as testing the interface, you need to test at least three internal invariants after each operation: - that the tree is balanced with respect to the balance condition, - that the meta-data used to maintain the balance condition is correct, and - that the tree is a binary search tree (i.e. that the keys are in sorted order if you do an inorder traversal). For this simple example, one extra exported function should do the trick: structuralInvariantFM :: (Ord k) => FiniteMap k v -> Bool However, a more complex data structure with multiple invariants would require even more exported functions, because it would become more important to know which invariant was broken. Cheers, Andrew Bromage