extrapolate: generalize counter-examples of test properties

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Extrapolate is a tool able to provide generalized counter-examples of test properties where irrelevant sub-expressions are replaces with variables.

For the incorrect property xs -> nub xs == (xs::[Int]):

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Versions0.0.1, 0.0.1, 0.1.0, 0.2.0, 0.2.1, 0.2.2, 0.2.3, 0.2.4, 0.3.0, 0.3.1, 0.3.2, 0.3.3, 0.4.0, 0.4.1
Change logNone available
Dependenciesbase (==4.9.*), leancheck, speculate, template-haskell [details]
AuthorRudy Matela
MaintainerRudy Matela <rudy@matela.com.br>
Home pagehttps://github.com/rudymatela/extrapolate#readme
Source repositoryhead: git clone https://github.com/rudymatela/speculate
this: git clone https://github.com/rudymatela/speculate(tag v0.0.1)
UploadedTue Aug 1 13:51:21 UTC 2017 by rudymatela




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Readme for extrapolate-0.0.1

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Extrapolate Build Status Extrapolate on Hackage

Extrapolate automatically generalizes counter-examples to test properties.


Consider the following (faulty) sort function and property:

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
  count x = length . filter (== x)

Extrapolate both 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]
x (x:x:xs)

This hopefully makes it easier to find the source of the bug. In this case, the faulty sort function discard repeated elements.

More documentation

For more examples, see the eg folder.