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林子篆

Posted on • Originally published at dannypsnl.github.io on

How to test in Haskell: HSpec setup

#haskell #beginners #testing

Before you start to read, ensure you're using Cabal >= 3.0 to manage your project.

For a Haskell project, I usually use Cabal, do not have any special reason. In the xxx.cabal file, we can define some common dependencies by common block:

-- just let you know how does the file should look like -- with full content people can understand the structure better cabal-version: 3.0 name: your-module version: 0.1.0.0 license: MIT license-file: LICENSE author: your-name maintainer: your-name@email.com -- Extra files to be distributed with the package, such as examples or a -- README. extra-source-files: CHANGELOG.md -- Common block common shared-properties default-language: Haskell2010 build-depends: base == 4.*, mtl >= 2.2 ghc-options: -Wall
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Then we can add test-suite block like this:

-- common block at here library import: shared-properties exposed-modules: YourModule other-modules: -- Directories containing source files. hs-source-dirs: src default-language: Haskell2010 test-suite spec import: shared-properties type: exitcode-stdio-1.0 other-modules: YourModuleSpec SpecHelper hs-source-dirs: test main-is: Spec.hs build-depends: hspec >= 2.7 , hspec-discover >= 2.7 , your-module default-language: Haskell2010
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Create $project-path/test/Spec.hs and put:

{-# OPTIONS_GHC -F -pgmF hspec-discover #-}
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And create $project-path/test/SpecHelper.hs and put:

module SpecHelper ( module Test.Hspec ) where import Test.Hspec
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Finally, create $project-path/test/YourModuleSpec.hs and put:

module YourModuleSpec where import SpecHelper import YourModule spec :: Spec spec = describe "Your module" $ do context "has a function add can add two nature numbers" $ do (add 1 2) `shouldBe` 3 main :: IO () main = hspec spec
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Then run commands:

cabal new-update cabal new-install --only-dependencies cabal install hspec-discover cabal new-configure --enable-tests cabal new-test
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We finish the setup of testing now.

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