Extrapolate
===========
[![Extrapolate Build Status][build-status]][build-log]
[![Extrapolate on Hackage][hackage-version]][extrapolate-on-hackage]
Extrapolate is a property-based testing library for Haskell
capable of reporting generalized counter-examples.
Example
-------
Consider the following (faulty) sort function and a property about it:
sort :: Ord a => [a] -> [a]
sort [] = []
sort (x:xs) = sort (filter (< x) xs)
++ [x]
++ sort (filter (> x) xs)
prop_sortCount :: Ord a => a -> [a] -> Bool
prop_sortCount x xs = count x (sort xs) == count x xs
where
count x = length . filter (== x)
After testing the property, Extrapolate returns a fully defined counter-example
along with a generalization:
> import Test.Extrapolate
> check (prop_sortCount :: Int -> [Int] -> Bool)
*** Failed! Falsifiable (after 4 tests):
0 [0,0]
Generalization:
x (x:x:xs)
This hopefully makes it easier to find the source of the bug. In this case,
the faulty sort function discards repeated elements.
More documentation
------------------
For more examples, see the [eg](eg) folder.
[build-status]: https://travis-ci.org/rudymatela/extrapolate.svg?branch=master
[build-log]: https://travis-ci.org/rudymatela/extrapolate
[hackage-version]: https://img.shields.io/hackage/v/extrapolate.svg
[extrapolate-on-hackage]: https://hackage.haskell.org/package/extrapolate