How to test a rails PORO called from controller - ruby-on-rails

Question

I have extracted part of my Foos controller into a new rails model to perform the action:
foos_controller.rb
class FoosController < ApplicationController
respond_to :js
def create
#foo = current_user.do_something(#bar)
actioned_bar = ActionedBar.new(#bar)
actioned_bar.create
respond_with #bar
end
actioned_bar.rb
class ActionedBar
def initialize(bar)
#bar = bar
end
def create
if #bar.check?
# do something
end
end
end
I got it working first but now I'm trying to back-fill the rspec controller tests.
I'll be testing the various model methods and will be doing a feature test to make sure it's ok from that point of view but I would like to add a test to make sure the new actioned_bar model is called from the foos controller with #bar.
I know in rspec you can test that something receives something with some arguments but I'm struggling to get this to work.
it "calls ActionedBar.new(bar)" do
bar = create(:bar)
expect(ActionedBar).to receive(:new)
xhr :post, :create, bar_id: bar.id
end
This doesn't work though, the console reports:
NoMethodError:
undefined method `create' for nil:NilClass
which is strange because it only does this when I use expect(ActionedBar).to receive(:new), the rest of the controller tests work fine.
If I try to do:
it "calls ActionedBar.new(bar)" do
bar = create(:bar)
actioned_bar = ActionedBar.new(bar)
expect(actioned_bar).to receive(:create).with(no_args)
xhr :post, :create, bar_id: bar.id
end
the console says:
(#<ActionedBar:0xc8f9f74>).create(no args)
expected: 1 time with no arguments
received: 0 times with no arguments
If I do a put in the controller whilst running the test; for some reason this test causes the actioned_bar in the controller to be output as nil but fine for all the other controller tests.
Is there any way I can test that ActionedBar is being called in this controller spec?

Answer 1

You can use expect_any_instance_of(ActionedBar).to receive(:create), because instance in spec and in controller are different instances.
If you want to use original object, you can use expect(ActionedBar).to receive(:new).and_call_original (without that #new just will return nil and you'll get NoMethodError).

Answer 2

You can set up a double ActionedBar which is returned by the ActionedBar.new call as this instance is different to the one used in the controller.
describe "#create" do
let(:actioned_bar) { double(ActionedBar) }
let(:bar) { double(Bar) }
it "calls ActionedBar.new(bar)" do
expect(ActionedBar).to receive(:new).with(bar).and_returns(actioned_bar)
expect(actioned_bar).to receive(:create)
xhr :post, :create, bar_id: bar.id
end
end

Answer 3

The core problem is that actioned_bar in your spec in is not going to be the the same instance of ActionedBar that is in your controller. Thus the spec will always fail.
Instead you need to have ActionedBar return a double when new is called:
it "calls ActionedBar.new(bar)" do
bar = create(:bar)
actioned_bar = instance_double("ActionedBar")
allow(ActionedBar).to receive(:new).and_return(actioned_bar)
expect(actioned_bar).to receive(:create).with(no_args)
xhr :post, :create, bar_id: bar.id
end
However I generally consider this kind of test a code smell - its ok to mock out external collaborators and set expectations that you are passing the correct messages. But your might want to consider if your are testing the details of how your controller does its job and not the actual behavior.
I find it better to setup a spec which calls the controller action and set expectations on what how it for example changes the database state or how it effects the response.