Why not use smallcheck?

turion:

For your specific example, for a threshold of 18, tinycheck finds the bug after less than 2 million (and more than 200 000) values, which takes 0.3 seconds on my machine. (1.4 seconds for a threshold of 20, still less than 2 million values.) I agree that this is probably less performant than QuickCheck, but still I find it noteable. I achieved it by just writing down the basic idea behind SmallCheck from memory in little time as a library. This says something about the power of the idea.

You asked me about SmallCheck, not about your library. Here is a test suite I based my previous answer on:

#!/usr/bin/env cabal
{- cabal:
build-depends: base, tasty, tasty-smallcheck
default-language: GHC2021
-}

import Test.Tasty
import Test.Tasty.SmallCheck
import Data.List (sort)

main = defaultMain $
  -- depth 19 means that we are building lists of length 0..18
  localOption (SmallCheckDepth 19) $
    testProperty "mySort matches the reference implementation" $
      \xs -> mySort xs == sort xs

mySort :: [Int] -> [Int]
mySort xs
  | length xs < 18 = sort xs
  | otherwise = error "explode"

This completed ~65000 of tests in 10 minutes on my machine and does not seem to be anywhere near the counterexample. If your library completes 200000+ tests in 0.3 seconds (which is roughly 6000 times faster), that’s a great result, but it does not relate to SmallCheck.