In an attempt to clarify what the controller makes available to views instead of guessing, identify them with #expose

application_controller.rb

#Include this method in your application_controller.rb
def self.expose(*variable_names)
  variable_names.each do |variable_name|
    define_method((variable_name.to_s+"=").to_sym) do |value|
      @exposed ||= Hash.new
      @exposed[variable_name]= value
    end
    private (variable_name.to_s+"=").to_sym

    define_method(variable_name) do
      @exposed ||= Hash.new
      Maybe(@exposed[variable_name])
    end

    helper_method variable_name
  end
end

example_controller_spec.rb

require 'rspec/given'

describe MyOrdersController
  describe "#open" do
    context "when the orders repository finds a few orders" do
      Given (:array_of_orders) { mock }
      Given { OrdersRepository.stub(:find_open).and_return(array_of_orders) }
      When  { get :open }
      Then  { expect(controller).to expose(array_of_orders).as(:orders) }
    end
  end
end 

example_controller_usage.rb

class MyOrdersController < ApplicationController
  expose :orders
  
  def open
    self.orders = OrdersRepository.find_open
  end
end

expose_matcher.rb

RSpec::Matchers.define :expose do |value|
  match do |actual|
    actual.send(@getter) == value
  end

  chain :as do |getter|
    @getter = getter
  end

  failure_message_for_should do
    "should have exposed #{value} to the view as '#{@getter}'"
  end

  failure_message_for_should_not do
    "should not have exposed #{value} as '#{@getter}'"
  end

  description do
    "should expose #{value} to the view as '#{@getter}'"
  end
end

Not entirely happy with the implementation of the expose method, but it works for now. The spec matcher and usage capture the essence of what I am trying to achieve.

  expose :value1, :value2, :etc

  expect(controller).to expose(some_value).as(variable_name)