Sorry I'm late to the party...but there are some things about this message that confuse me:

* `errors_on` has been moved to `rspec-collection_matchers` so the user can't use it w/o loading that gem at which point they might as well keep the expectation the same and not re-write it, right?  I'm not actually sure what the replacement is since I don't know the activemodel API well.
* Doesn't `errors_on` require an argument (e.g. `errors_on(:name)`)?  It's confusing to me to see it used without the argument