Using 'should throw' or 'should throwWithMessage' never succeeds unless function returns unit

Description

This is related to #214, but not the same.

The following test always fails:

[<Fact>]
let ``Test raising exception`` () =
    fun () -> raise (ArgumentException "help")
    |> should (throwWithMessage "help") typeof<ArgumentException>

Repro steps

See above.

Expected behavior

Test should succeed.

Actual behavior

Test fails with the following message:

Message: 
   FsUnit.Xunit+MatchException : Exception of type 'FsUnit.Xunit+MatchException' was thrown.
   Expected: System.ArgumentException "help"
   Actual:   <fun:Test raising exception@127>

Known workarounds

The following fixes the test, but this is not obvious. I should note that in the FsUnit help pages, all examples include ignore, but this isn’t obvious and it took me a while to figure out what was wrong with my test (after our discussion in #214.

[<Fact>]
let ``Test raising exception`` () =
    fun () -> raise (ArgumentException "help") |> ignore
    |> should (throwWithMessage "help") typeof<ArgumentException>

Related information

There may be a reason why ignore is required in such tests. But if there’s some way that this isn’t required, I think that would be awesome: mainly because it isn’t trivial to figure this out once it hits you.

PS: great work on fixing and maintaining this lib! It’s generally a breeze to use!

[abelbraaksma]

you don’t need ignore anymore as in your opening post:

exactly, but…

Also on functions that return obj or a generic type 'a. That is valid for throwWithMessage.

this didn’t work

tested it with throw without ignore, that test failed for xUnit. I’ll put it on my list (https://github.com/fsprojects/FsUnit/issues/225).

Awesome, tx!

[CaptnCodr]

Hey @abelbraaksma, thanks for the little repro, I’ll look at it this week. 🙂