gistfile1.hs

newtype LanguageDBState = LanguageDBState { expandState :: (String, [LoadedEntity Language]) }
          deriving (Show)

instance Arbitrary LanguageDBState where
  arbitrary =
    elements [
      LanguageDBState
      ( [str| INSERT INTO language (iso_code, name) VALUES ('eng', 'English') |]
      , [Entity { entityRef = Ref (toSql ("eng" :: String))
                , entityInfo = Language { languageName = "English"
                                        , languageIsoCode = "eng" } }]
      )
    ]

prop_language_allLanguages = monadicIO $ do
  (sql, languages) <- expandState `fmap` (pick arbitrary :: PropertyM IO LanguageDBState)
  fetched <- run $ databaseTest $ (runRaw sql >> allLanguages)
  assert $ fetched == languages