How to access a Rails controller view context from outside of a controller?

Question

I am working on cleaning up some code that relies on some custom controller helper methods, by creating a "plain old Ruby" presenter object. In my controller, I am able to pass the view context to the class:

def show
  # old code: view_context.bad_helper_method
  @foobar = FoobarPresenter.new(Foobar.find(params[:id]), view_context)
end

class FoobarPresenter
  def initialize(model, view_context)
    @model = model
    @view_context = view_context
  end

  def something
    @view_context.bad_helper_method
  end
end

However, I'm not sure what to pass in my test. I would rather pull the helper/view_context dynamically so that I don't have to pass it in.

How can I access the view/controller helper context outside of the controller?

This is a Rails 3.2 project.

Answer 1

Simpler than you think! (I lost almost an hour until I found a way)

You can instantiate an ActionView

_view_context = ActionView::Base.new

and use it in your test

FoobarPresenter.new(Foobar.new, _view_context)

Answer 2

How about testing the expectations?

1. Test for controller (note that subject is the instance of the controller, assuming we're testing using rspec-rails):

   view_context     = double("View context")
   foobar_presenter = double("FoobarPresenter")
   
   allow(subject).to receive(:view_context).and_return(view_context)
   allow(FoobarPresenter).to receive(:new).with(1, view_context).and_return(foobar_presenter)
   
   get :show, id: 1
   
   expect(assigns(:foobar)).to eql(foobar_presenter)
   

2. Test for presenter:

   view_context = double('View context', bad_helper_method: 'some_expected_result')
   presenter    = FoobarPresenter.new(double('Model'), view_context)
   
   expect(presenter.something).to eql('some_expected_result')
   

Answer 3

I unfortunately don't have a perfect answer for you. However, I've dug through the Draper Decorator library, and they have solved this problem.

In particular, they have a HelperProxy class and a ViewContext class that seem to automatically infer the context that you want.

https://github.com/drapergem/draper

They also have some specs around both of these classes, which I'm sure you could borrow from in setting up your own specs.