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Fun state_machine rspec gotcha

Let’s say you’ve got the following:

class Thing  :draft do
    event :publish do
      transition all => :published
    end
     state :published do
      validates_presence_of :author
    end
  end
end

You want to test your validations on the state transition like so:

it "requires an author to transition to published" do
    thing = Thing.new
    thing.author.should be_nil
    thing.publish
    thing.should have(1).error_on(:author)
end

This test fails. Why? 1) When a state_machine transition fails, it automatically rolls you back to the prior state. 2) The prior state will now be valid, as we don’t have the extra validations added by state machine. Calling valid? at this point will clear out the (correct) errors that state_machine added to your object when it tried to transition it. 3) error_on calls valid? under the hood. This seems to have implications for controllers too — you’d never want to change a state and then save, you’d always want to thing.save if (thing.publish). An interesting gotcha that confounded me for a bit, particularly since the internals of state_machine tend towards the meta. Eventually I just poked at my model in a console until I figured out what was going on.