auto #valid? good or bad idea for tests?

I've recently added this to the bottom of my test_helper.rb (it should really be in its own file, but first I want to get feedback):

module ActiveRecord   class Errors       alias_method :old_on, :on       def on(attribute)         self.instance_variable_get("@base").send :valid?         old_on(attribute)       end   end end

This alows me to avoid calling #valid? manually in every test where I am checking for a validation error:

topic = Topic.new assert_equal topic.errors.on(:title), "must be set"

Instead of:

topic = Topic.new topic.valid? assert_equal topic.errors.on(:title), "must be set"

I know that doesnt look like a huge deal, but when you have many tests which need to do something like this all the #valid? calls get ugly and repetetive. So, I'm looking for a reason anyone may have as to why this would be a bad idea. Im hoping no one can come up with reasons why it would be a bad idea, but if there are some I'd rather find out now.

Joe