Documentation

This combinator gives the programmer a lot of power. In fact, it gives the programmer enough power to break the test framework. Indeed, you can provide a wrapper function that just _doesn't_ run the function like this:

spec :: Spec
spec = do
   let don'tDo :: IO () -> IO ()
       don'tDo _ = pure ()
   aroundAll_ don'tDo $ do
     it "should pass" True

During execution, you'll then get an error like this:

thread blocked indefinitely in an MVar operation

The same problem exists when using around_.

Something even more pernicious goes wrong when you run the given action more than once like this:

spec :: Spec
spec = do
   let doTwice :: IO () -> IO ()
       doTwice f = f >> f
   aroundAll_ doTwice $ do
     it "should pass" True

In this case, the test will "just work", but it will be executed twice even if the output reports that it only passed once.

Note: If you're interested in fixing this, talk to me, but only after GHC has gotten impredicative types because that will likely be a requirement.