Rewriting to Haskell–Testing

Posted on April 13, 2020 by Riccardo

Rewriting to Haskell (Series)

Rewriting to Haskell–IntroRewriting to Haskell–Project SetupRewriting to Haskell–DeploymentRewriting to Haskell–Automatic FormattingRewriting to Haskell–ConfigurationRewriting to Haskell–Standing on the shoulders of RailsRewriting to Haskell–Making GHC More NitpickyRewriting to Haskell–TestingRewriting to Haskell–LintingRewriting to Haskell–Parsing Query ParamsRewriting to Haskell–Parsing Query Params, AgainRewriting to Haskell–Errors

We have managed to delay testing by leaning on Ruby RSpec for a while. It's time to do the right thing and write some tests in Haskell.

We peaked at the "How To Test Servant Applications" cookbook page and decided to go the hspec-wai way. In fact, using servant-client seemed a bit too involved and coupled with Servant. The former, on the other hand, enables us to test any wai application.

With that in mind we created a test/Spec.hs:

main :: IO ()
main = do
  setEnv "DATABASE" "stream_test"
-- ^ See for the why.
  application <- configuredApp
  connection <- getConnection
  hspec $ spec application connection

spec :: Application -> Connection -> Spec
spec application connection = with (pure application) $ after_ (truncateTables connection)
--                                                      ^ After each spec item truncate tables.
  $ describe "GET /servant/search"
  $ do
    it "with no query it returns all posts ordered by descending creation date" $ do
      user <- liftIO . createUser $ connection
      now <- liftIO randomUTCTime
      let later = addUTCTime 1 now
      let olderPostAttributes =
              { postAttributesUserId = userId user,
                postAttributesCreatedAt = Just now
      let newerPostAttributes = olderPostAttributes {postAttributesCreatedAt = Just later}
      olderPost <- liftIO $ createPost connection olderPostAttributes
      newerPost <- liftIO $ createPost connection newerPostAttributes
      get "/servant/search"
        `shouldRespondWith` [json|
--                          ^ Using hspec-wai-json and some Template Haskell to generate JSON.
        { users: [#{user}],
--                ^ Behind the curtains aeson-qq is used. Thus, you can interpolate variables:
          attachments: [],
          comments: [],
          posts: [#{newerPost}, #{olderPost}]

-- ...

At the moment we are just testing through the endpoints as shown above. Stream is a simple application so we feel confident with this approach. Should the need for other types of tests arise, then HSpec will have our backs.


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