On 2012-05-28, at 7:59 AM, Frank Shearar wrote:

>> That would be a nice property, but hash functions are not injective. If they
>> were, then either the codomain would be too large (not SmallInteger in our
>> case, which makes hashing impractical) or there were no need for the use of
>> hashing at all, since there were no collisions.
> 
> Sure, collisions mean that you can have a ~= b and yet a hash = b
> hash. Nevertheless, CompiledMethod define: #hash as: [^ 1] satisfies
> the above test, so on its own it's insufficient. I wouldn't ask for
> testing CM x CM  - {CompiledMethods whose hashes collide} !

So, essentially, you want a test that ensures that we have a high-quality hash function. That would be nice, but I'm not sure it fits into the structure of a unit test. Porting Andres' hash function tools to Squeak would probably be the best way to do that. Short of that, I'd suggest a simple smoke test - say, asserting that there are few collisions between the methods of TestCase or something like that.

Colin