是否可以在IO以外的monad中使用带有测试框架的HUnit？

Question

I currently have the following test code:

testUpdate :: Test
testUpdate = testCase "update does change artist" $ do
  (created, Just revised, parents) <- mbTest $ do
    Just editor <- fmap entityRef <$> findEditorByName "acid2"

    created <- create editor startWith
    let artistId = coreMbid created

    newRev <- update editor (coreRevision created) expected

    editId <- openEdit
    includeRevision editId newRev
    apply editId

    found <- findLatest artistId
    parents <- revisionParents newRev

    return (created, found, parents)

  coreData revised @?= expected

  assertBool "The old revision is a direct parent of the new revision" $
    parents == [coreRevision created]

  where
    startWith = ...
    expected = ...

This kinda works, but it's messy. I'd much rather be able to write something without having to return the various things under test, and instead have the assertions where they make sense.

I see there is the Assertable class, but it seems like I'd probably have to end up reinventing a bunch of stuff.

Answer 1

Why not just have your monad return an IO computation of type IO a , which is a pure value? Since as in your comment, the case where the monad is an instance of MonadIO is trivial, assume that the monad allows pure computation:

newtype M a = M {runM :: ....}
instance Monad M where
  ...

makeTest :: M Assertion
makeTest = do
    created <- ..
    found   <- ..
    parents <- ..
    let test1 = coreData revised @?= expected
    ...
    let test2 = assertBool "The old revision..." $
                   parents == [coreRevision create]

    return $ test1 >> test2

testUpdate :: Test
testUpdate = testCase "update does change artist" $ runM makeTest

A bonus is that you could return a collection of tests by one monadic computation, just as you would in the list monad.