Sometimes you might want to test a function that uses an HTTP client object to
get responses from some web server, without actually making the HTTP requests.
-- BEGINNING OF EXAMPLE
import Control.Monad.IO.Class
import Data.IORef
import Data.Maybe
import Test.Hspec
import Test.Pull.Fake.IO
data Request = Request
{ searchTerm :: String
, pageSize :: Int
, cursor :: Maybe String
} deriving (Eq, Show)
data Response = Response
{ searchResult :: [String]
, nextCursor :: Maybe String
} deriving (Eq, Show)
-- | The function you test.
-- Call `sendRequest` repeatedly to get all paginated search results using
-- the cursor.
fetchAllPages :: MonadIO m => (Request -> m Response) -> String -> m [String]
fetchAllPages sendRequest term = go [] (Request term 3 Nothing)
where
go accum req = do
res <- sendRequest req
let newAccum = accum ++ searchResult res
case nextCursor res of
Just cur -> do
let newReq = req { cursor = Just cur }
go newAccum newReq
Nothing -> return newAccum
-- | The function to make an HTTP request actually. Will be stubbed.
sendRequestActually :: Request -> IO Response
sendRequestActually = error "This function should be stubbed!"
-- | Simulate the `sendRequest` function that returns a different result every
-- time.
stubbedSendRequest :: FakeStream Response -> Request -> IO Response
stubbedSendRequest stream _request =
-- NOTE: You may want to validate the request argument for testing.
-- I've omitted that for simplicity here.
fromJust <$> pull stream
main :: IO ()
main = hspec $
describe "fetchAllPages" $
it "collect all results by sending requests" $ do
let allResponses =
[ Response ["result 1-1", "result 1-2", "result 1-3"] $ Just "cursor a"
, Response ["result 2-2", "result 2-2", "result 2-3"] $ Just "cursor b"
, Response ["result 3-1"] Nothing
]
responsesToReturn <- newFakeStream allResponses
fetchAllPages (stubbedSendRequest responsesToReturn) "result"
`shouldReturn` concatMap searchResult allResponses
-- END
