Was there a reason this got abandoned? Is it something I could pick up and finish off?

I found myself wanting to do an .Is assertion today, and although it works with .Check()/.Assert() the default failure message isn't great as it doesn't tell you what error you got instead

There is https://pkg.go.dev/gotest.tools/v3/assert#ErrorType, but erorrs.Is does compare a bit differently.

I'll run CI again to see what state this is in. From the previous runs it looks like I probably put this on hold because I wasn't too sure what the failure messages should look like. I guess that would probably be the last thing to figure out before getting this merged.

Ah, I've checked the branch out and I see what you mean.

Potentially for Is the useful information is?

• expected: The message and type (or maybe not the type if it's only an errorString?)
• source: The message and its whole chain of wrapped types?

I rebased this again and fixed the tests.

Removing errors.errorString might be nice, but probably ok to keep it for now. Since that type isn't exported the name could change, so excluding it by name might not be reliable.

I guess we could also print all the wrapped types. Right now it's only printing the top-level type along with the name of the symbol and error message.

I marked this as ready for review. If you don't have a need for the full chain of wrapped types I'd be fine to merge this as-is and we could look at adding it later. But if you are interested in adding that to the message I can keep this open for a bit.

Thanks for the nudge to get this included, and for giving it a review!