hstest looks through all Haskell source files in the current directory (by default), runs all properties via QuickCheck 1
(properties must have a name that starts prop_), and runs all tests via HUnit (tests must have a name that starts test_).
For example, suppose you have this Haskell source file called mysort.hs:
mySort xs = ... -- a function you wish to test (definition elided)
prop_lengthStaysTheSame xs = length xs == length (mySort xs)
prop_sumStaysTheSame xs = sum xs == sum (mySort xs)
prop_lowestElementAtStart, prop_highestElementAtEnd :: [Int] -> Bool
prop_lowestElementAtStart xs = not (null xs) ==> minimum xs == head (mySort xs)
prop_highestElementAtEnd xs = not (null xs) ==> maximum xs == last (mySort xs)
Then to check all these tests, you run
$ hstest
Failed prop_highestElementAtEnd:
* [-3,2,-2]
mysort.hs: Failed 1 property, passed 3 properties
Oops! Fix mySort and try again:
$ hstest
mysort.hs: Passed 4 properties
