leancheck-1.0.2: Enumerative property-based testing
Copyright(c) 2015-2024 Rudy Matela
License3-Clause BSD (see the file LICENSE)
MaintainerRudy Matela <rudy@matela.com.br>
Safe HaskellSafe-Inferred
LanguageHaskell2010

Test.LeanCheck.Function

Description

This module is part of LeanCheck, a simple enumerative property-based testing library.

This module exports Listable and Show function typeclass instances. These can be useful for testing higher-order properties --- properties that take functions as arguments.

> import Test.LeanCheck
> import Test.LeanCheck.Function
> check $ \f p xs -> filter p (map f xs) == map f (filter p xs :: [Int])
*** Failed! Falsifiable (after 36 tests):
\_ -> 0
\x -> case x of
      0 -> True
      _ -> False
[1]
> check $ \f p xs -> filter p (map f xs) == map f (filter p xs :: [Bool])
*** Failed! Falsifiable (after 20 tests):
\_ -> False
\x -> case x of
      False -> False
      True -> True
[True]
> check $ \f z xs -> foldr f z xs == foldl f z (xs :: [Int])
*** Failed! Falsifiable (after 75 tests):
\x _ -> case x of
        0 -> 1
        _ -> 0
0
[0,0]

Warning: this is only intended to be used in testing modules. Avoid importing this on modules that are used as libraries.

The Listable and Show function instance are defined in, respectively:

The Show instance will work for all functions whose return types are instances of ShowFunction from Test.LeanCheck.Function.ShowFunction.