Add assertThrows

[hdgarrood]

I'm currently trying to improve the compiler test suite, and so this is to replace assertPartial in the test prelude. This will probably be useful more generally too, though.

[garyb]

Could you add a comment to the new function(s) please? Also, shouldn't we be using Eff (err :: EXCEPTION | eff) there rather than Unit -> a really?

[hdgarrood]

The idea behind this was, if you have something which is Eff (err :: EXCEPTION | eff) a, then it's easy to check whether it throws an exception, using catchException. On the other hand, there's no obvious way to check whether "pure" code will throw an exception.

[garyb]

In what situation would you want pure code to throw an exception? 😄

[hdgarrood]

To make sure that an unsafe function does what you want it to? Eg assertThrows $ unsafeIndex -1 xs? The specific use case I was thinking of is here: https://github.com/purescript/purescript/blob/master/examples/passing/PartialFunction.purs

[garyb]

Gotcha, that makes sense. Perhaps we should mention something like that in the comment too then ("this is for testing unsafe functions" or whtever), as I think assertThrows actually can't be used to test Eff-based exceptions with this type signature.

[hdgarrood]

👍

[garyb]

Great, thanks!

Oh, er, one last thing - can you remove the import Control.Monad.Eff.Exception (EXCEPTION())? It's breaking in travis as -assert doesn't depend on -exceptions currently 😉

[garyb]

👍