Generalize assertion function types for return types and monad

[osa1]

Literally every single test suite I work on needs these two:

• Assertion functions that work in any MonadIO. With this I can use same assertion functions in different test monads, e.g. the monad in hspec-webdriver.

• Assertion functions with generalized return value. Something like

type Assertion' a = IO a

assertFailure :: HasCallStack => String -> Assertion' a

Now I can use this in cases like

x <- case doX of
       T1 -> assertFailure "doX returned T1!"
       T2 x -> return x

Since these additions are so small I usually end up copying same code snippets to every single project I work on. I think these would be great additions to HUnit and other people would also benefit it.

[sol]

For assertions/expectations generalized to MonadIO you can use hspec-expectations-lifted.

It's not suitable as a default because it hurts type inference in Hspec.

[sol]

I'm ok with changing the type of assertFailure:

assertFailure :: HasCallStack => String -> IO a

[osa1]

Nice, I didn't know about hspec-expectations-lifted, thanks.

You originally wrote "PR please" but do you still want a PR or are you going to do this yourself?

[sol]

Yes, PR please.