Haskell unit testing

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Generally, any significant Haskell project is run with Cabal. This takes care of building, distribution, documentation (with the help of haddock), and testing.

The standard approach is to put your tests in the test directory and then set up a test suite in your .cabal file. This is detailed in the user manual. Here’s what the test suite for one of my projects looks like

Test-Suite test-melody
  type:               exitcode-stdio-1.0
  main-is:            Main.hs
  hs-source-dirs:     test
  build-depends:      base >=4.6 && <4.7,
                      test-framework,
                      test-framework-hunit,
                      HUnit,
                      containers == 0.5.*

Then in the file test/Main.hs

import Test.HUnit
import Test.Framework
import Test.Framework.Providers.HUnit
import Data.Monoid
import Control.Monad
import Utils

pushTest :: Assertion
pushTest = [NumLit 1] ^? push (NumLit 1)

pushPopTest :: Assertion
pushPopTest = [] ^? (push (NumLit 0) >> void pop)

main :: IO ()
main = defaultMainWithOpts
       [testCase "push" pushTest
       ,testCase "push-pop" pushPopTest]
       mempty

Where Utils defines some nicer interfaces over HUnit.

For lighter-weight testing, I strongly recommend you use QuickCheck. It lets you write short properties and test them over a series of random inputs. For example:

 -- Tests.hs
 import Test.QuickCheck

 prop_reverseReverse :: [Int] -> Bool
 prop_reverseReverse xs = reverse (reverse xs) == xs

And then

 $ ghci Tests.hs
 > import Test.QuickCheck
 > quickCheck prop_reverseReverse
 .... Passed Tests (100/100)

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