import Control.Concurrent (forkIO, newEmptyMVar, putMVar, takeMVar) import Control.Monad (replicateM, void) import Data.Foldable (for_) import Data.Traversable (for) import Data.Maybe (isNothing, catMaybes) import Test.Hspec (Spec, it, shouldReturn) import Test.Hspec.Runner (configFailFast, defaultConfig, hspecWith) import BankAccount ( closeAccount , incrementBalance , getBalance , openAccount ) main :: IO () main = hspecWith defaultConfig {configFailFast = True} specs specs :: Spec specs = do it "checks that a new account is initialized to 0" $ do account <- openAccount getBalance account `shouldReturn` Just 0 closeAccount account it "sequentially increments an account then checks the balance" $ do account <- openAccount getBalance account `shouldReturn` Just 0 incrementBalance account 10 `shouldReturn` Just 10 incrementBalance account 20 `shouldReturn` Just 30 getBalance account `shouldReturn` Just 30 closeAccount account it "concurrently increments an account then checks the balance" $ do let nThreads = 50 account <- openAccount vs <- replicateM nThreads $ do v <- newEmptyMVar void $ forkIO $ do void $ incrementBalance account 1 putMVar v () return v for_ (reverse vs) takeMVar getBalance account `shouldReturn` Just (toInteger nThreads) closeAccount account it "concurrently increments an account AND checks the balance" $ do let nThreads = 50 account <- openAccount vs <- replicateM nThreads $ do v <- newEmptyMVar void $ forkIO $ do i <- incrementBalance account 1 b <- getBalance account putMVar v [ if isNothing i then Just "Failed to increment!" else Nothing , if isNothing b then Just "Failed to get balance!" else Nothing ] return v fmap (catMaybes . concat) (for vs takeMVar) `shouldReturn` [] getBalance account `shouldReturn` Just (toInteger nThreads) closeAccount account it "checks that a closed account holds nothing" $ do account <- openAccount getBalance account `shouldReturn` Just 0 incrementBalance account 15 `shouldReturn` Just 15 closeAccount account getBalance account `shouldReturn` Nothing incrementBalance account 10 `shouldReturn` Nothing