On Tue, Apr 16, 2013 at 2:45 PM, Dan
I've discovered the excellent proxy library recently and one thing strikes me. How do you unit test a proxy? Are there any specific methods or workflows for doing this cleanly and consistently?
I don't think it's different from testing other normal Haskell code. And as such, you will need to consider the particulars of the base monad you are using for your proxies. For example, if your base monad is 'IO', then you should reason about your unit tests and properties the same way you would for any other non-pipes 'IO' code you test. Below is a simple working example that tests a simple proxy using both HUnit and QuickCheck. I find the 'toListD' Proxy particularly useful in cases like these. module Main where import Control.Proxy ((>->)) import qualified Control.Proxy as P import Test.HUnit import Test.QuickCheck -- | This Proxy doubles Int values flowing downstream. doublerD :: (Monad m, P.Proxy p) => a' -> p a' Int a' Int m r doublerD = P.mapD (*2) -- | A unit test about 'doublerD' test_doublerD :: Test test_doublerD = [2,4,6] ~=? actual where actual = let session = P.fromListS [1,2,3] >-> doublerD >-> P.toListD in head . P.execWriterT . P.runProxy $ session -- | A property we can test about 'doublerD' using QuickCheck prop_doublerD :: [Int] -> Bool prop_doublerD xs = expected == actual where expected = fmap (*2) xs actual = let session = P.fromListS xs >-> doublerD >-> P.toListD in head . P.execWriterT . P.runProxy $ session main :: IO () main = do putStrLn "HUnit tests:" >> runTestTT test_doublerD putStrLn "QuickCheck tests:" >> quickCheck prop_doublerD And the output, after running the code: HUnit tests: Cases: 1 Tried: 1 Errors: 0 Failures: 0 QuickCheck tests: +++ OK, passed 100 tests. Regards, Renzo Carbonara.