expect_error could handle the error class

[gaborcsardi]

I mean, I want to specify that I expect a given error class, instead of specifying the error message. AFAICT this is currently not possible.

[hadley]

Great idea. I'd be happy to review a PR :)

[hadley]

And presumably this should also cover warnings and messages. I'll have a go at it.

[hadley]

Oh messages() and warnings() are bit trickier because there might be more than one. I'll leave those for now.

[gaborcsardi]

Great! Thanks! This will allow proper error testing once we have proper error objects in R packages. :)