TestFixtureSpec.hs

{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE TemplateHaskell #-}

module Test.Control.Monad.TestFixtureSpec (spec) where

import Test.Hspec

import Control.Monad.Trans.Class (lift)
import Control.Monad.TestFixture
import Control.Monad.TestFixture.TH

newtype Id a = Id Int
newtype DBError = DBError () deriving (Eq, Show)

data HTTPRequest = GET String
data HTTPResponse = HTTPResponse { responseStatus :: Int }
data HTTPError

class DBRecord a where
  procureRecord :: a

data User = User deriving (Eq, Show)
instance DBRecord User where
  procureRecord = User

class Monad m => DB m where
  fetchRecord :: DBRecord a => Id a -> m (Either DBError a)
  insertRecord :: DBRecord a => a -> m (Either DBError (Id a))

class Monad m => HTTP m where
  sendRequest :: HTTPRequest -> m (Either HTTPError HTTPResponse)

class Monad m => Throw m where
  throwMessage :: String -> m a

useDBAndHTTP :: (DB m, HTTP m, DBRecord r) => r -> m (Either DBError r)
useDBAndHTTP record = do
  (Right (Id recordId)) <- insertRecord record
  (Right response) <- sendRequest $ GET ("/record/" ++ show recordId)
  fetchRecord $ Id (responseStatus response)

mkFixture "Fixture" [''DB, ''HTTP, ''Throw]

-- At compile time, ensure the fixture type synonyms are generated.
fixturePure :: FixturePure
fixturePure = def :: Fixture (TestFixture Fixture () ())

fixtureLog :: FixtureLog log
fixtureLog = def :: Fixture (TestFixture Fixture log ())

fixtureState :: FixtureState state
fixtureState = def :: Fixture (TestFixture Fixture () s)

fixtureLogState :: FixtureLogState log state
fixtureLogState = def :: Fixture (TestFixture Fixture log state)

fixturePureT :: Monad m => FixturePureT m
fixturePureT = def :: Fixture (TestFixtureT Fixture () () m)

fixtureLogT :: Monad m => FixtureLogT log m
fixtureLogT = def :: Fixture (TestFixtureT Fixture log () m)

fixtureStateT :: Monad m => FixtureStateT state m
fixtureStateT = def :: Fixture (TestFixtureT Fixture () s m)

fixtureLogStateT :: Monad m => FixtureLogStateT log state m
fixtureLogStateT = def :: Fixture (TestFixtureT Fixture log state m)

spec :: Spec
spec = do
  describe "mkFixture" $
    it "generates a fixture type that can be used to stub out methods" $ do
      let fixture = def
            { _fetchRecord = \_ -> return $ Right procureRecord
            , _insertRecord = \_ -> return $ Right (Id 42)
            , _sendRequest = \_ -> return $ Right (HTTPResponse 200)
            }
      let result = unTestFixture (useDBAndHTTP User) fixture
      result `shouldBe` Right User

  describe "handle throws" $ do
    it "capture a thrown error message" $ let
      throwFixture :: FixturePureT (Either String)
      throwFixture = def
        { _throwMessage = \msg -> lift (Left msg)
        }

      throwExample :: Throw m => m ()
      throwExample = throwMessage "error message"

      actual = unTestFixtureT throwExample throwFixture
      expected = Left "error message"
      in actual `shouldBe` expected