testing.md

Testing

QuickCheck

Property-based testing

import Test.QuickCheck

Function under test

reverse :: [a] -> [a]

Property of the function

double_reverse xs = reverse (reverse xs) == xs

Run it

Standard run

Prelude Test.QuickCheck> quickCheck double_reverse 
+++ OK, passed 100 tests.

Version for the curious

Prelude Test.QuickCheck> verboseCheck double_reverse
Passed:
[]
Passed:
[]
Passed:
[()]
Passed:
[(),()]
Passed:
[(),(),(),()]
...
Passed:
[(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),()]
+++ OK, passed 100 tests.

Also try

verboseCheck (prop_reverse :: [Int] -> Bool)

Non-abstract example

sumAbs = sum . map abs
prop_sumAbs xs = sumAbs xs == sum xs

It fails, who knew...

quickCheck prop_sumAbs
*** Failed! Falsifiable (after 4 tests and 2 shrinks):    
[-1]

HUnit

Tasty