Hello Haskell-café, I am happy to announce LeanCheck and Extrapolate, two enumerative property-based testing libraries (a.k.a. QuickCheck-style testing). https://hackage.haskell.org/package/leancheck https://hackage.haskell.org/package/extrapolate LeanCheck is a list-based enumerative property-based testing library with a very small core of only 180 lines of code. LeanCheck is somewhat stable and has actually been around for a while, but this is its first announcement on haskell-café. It works like so: $ ghci > import Test.LeanCheck > check $ \x y -> x + y == y + (x :: Int) +++ OK, passed 200 tests. Extrapolate works on top of LeanCheck, and its able to produce generalized counter-examples in addition to fully defined ones. Like so: $ ghci > import Test.Extrapolate > import Data.List (nub) > check $ \xs -> nub xs == (xs :: [Int]) *** Failed! Falsifiable (after 3 tests): [0,0] Generalization: x:x:_ Conditional Generalization: x:xs when elem x xs Extrapolate is under active development at the moment. To install both libraries, just: $ cabal update $ cabal install leancheck $ cabal install extrapolate They are also available on Stackage, installable via 'stack install': https://www.stackage.org/package/leancheck (lts-9 and nightly) https://www.stackage.org/package/extrapolate (just nightly) -- Rudy