Over a million developers have joined DZone.

A Simple TDD Environment in Haskell

DZone's Guide to

A Simple TDD Environment in Haskell

Learn the code to create a home for Test Driven Development in Haskell as well as where to get the resources to make it easier.

· Web Dev Zone
Free Resource

Should you build your own web experimentation solution? Download this whitepaper by Optimizely to find out.

I recently implemented the bowling kata in Haskell. In the process, I found out how set up my environment to comfortably do Test Driven Development. Hopefully, others might find this post helpful to begin their journey with the language. I used the following components:

  • Haskell installation: Haskell Platform. This also gives you GHCi which you can use as an interactive environment and type inspector.
  • IDE: Any editor would suffice, but I used Visual Studio Code as they have an extension for Haskell that gave me some basic IntelliSense features.
  • Test libraries: Hspec, which is based on RSpec. This can be installed using Haskell's package manager, cabal, from the command line with cabal install hspec.
  • Helper libraries: Printf for colourful command line output.

Using the example from Hspec's documentation, I began with this structure for my code:


module BowlingTests where

import Bowling

import Test.Hspec
import Text.Printf (printf)

testScoreGame :: String -> Int -> Spec
testScoreGame game score =
  it (printf “should return the score for game : %s → %d \n” game score) $
    scoreGame game `shouldBe` score

main = hspec $ do
  describe "scoreGame" $ do 
    testScoreGame "--------------------" 0

So to test a function, you add a function in your test file, usually the same name with a ‘test’ prefix. This function takes the inputs to your function under test and the expected output as parameters. Then using Hspec you describe what you are testing. As you can see the ‘it’ part is written in the test function. You can of course omit this helper function and write all your tests under main = hspec $ do, which may be nicer if you want to describe in more detail what each individual test is testing.


These files are in the same directory, now I can run my tests from the command line.

$ runhaskell BowlingTests.hs

should return the score for game : — — — — — — — — — — → 0

Finished in 0.0000 seconds
1 example, 0 failures

There you have it. Now I can focus on writing a failing test and making it pass.

This article was first published on the Codurance blog.

Implementing an Experimentation Solution: Choosing whether to build or buy?

components ,test driven development ,kata ,command line ,functional languages

Published at DZone with permission of Liam Griffin, DZone MVB. See the original article here.

Opinions expressed by DZone contributors are their own.

{{ parent.title || parent.header.title}}

{{ parent.tldr }}

{{ parent.urlSource.name }}