Question about expecting exceptions

[paulyoung]

Would it possible to expect exceptions via attributes?

Borrowing from NUnit, this might look like:

[<Property(ExpectedException="exn")>]

or

[<Property>]
[<ExpectedException("exn")>]

[paulyoung]

To clarify, this would allow:

[<Property(ExpectedException="exn")>]
let ``failure`` (e: exn) =
  Failure e |> dematerialize

vs

[<Property>]
let ``failure`` (e: exn) =
  Prop.throws<exn, _> (lazy (Failure e |> dematerialize))

[ploeh]

If this idea is the same as MSTest's [ExpectedException] attribute, everyone pretty much agrees that it was a bad idea. Here's one explanation: http://hadihariri.com/2008/10/17/testing-exceptions-with-xunit

I don't think it'd be a good idea to perpetuate a bad idea when there are better options around.

BTW, you should consider looking at Unquote for expressing assertions.

[paulyoung]

Thanks @ploeh, I'll look into that.

I tried using Unquote but it had some limitations that meant it wasn't an option for me.

[ploeh]

BTW, I hope the above comment wasn't too crass. I was on my way out the door when I wrote it, but now that I reread it, I think it looks a little impolite. If so, please accept my apologies.

[paulyoung]

Not at all! Nice to hear from you.

[kurtschelfthout]

Yeah, not a fan of that suggestion either. Been bitten a few too many times by overly broad attribute-based ExpectedException mechanisms.

Most unit testing frameworks should have support for somethink like Assert.Throws<ArgumentException(fun () -> ...) nowadays anyway. If not, it's easy to write.