should_change_with_action_test.rb

context "Given a bunch of stuff" do
  setup do
    @thing = Factory(:thingy)
    @user = Factory(:user)
    @user.register_with(@thing)
  end

  # THIS is the code I'm actually testing, isolated from the rest of the setup
  action("the user activates the thing") do
    @user.activate(@thing)
  end

  should_change("the thing's colour") { @thing.colour }

  should "not allow the thing to be activated again" do
    assert_raises(AlreadyActivated) { @user.activate(@thing) }
  end

  # etc...
end