Rails rspec with FactoryGirl and instance variables - ruby-on-rails

Question

I do not write tests very well and I have some trouble using instance variable from Application Controller for another controllers in test.
In Rails I had a pretty simple controller action.
def index
#cities = City.all
#starred_cities = #cities.where(starred: true)
end
For this action I have a test:
RSpec.describe CitiesController, :type => :controller do
let(:city) { create(:city) }
describe 'GET #index' do
let(:cities) { create_list(:city, 2) }
before { get :index }
it 'populates an array of all cities' do
expect(assigns(:cities)).to match_array(cities)
end
it 'renders index view' do
expect(response).to render_template :index
end
end
end
In application I need to get a country by domain name and set globally for all controllers. I add to ApplicationController before_action method like this:
before_action :get_country
def get_country
country_slugs = {en: 'usa', ru: 'russia', es: 'spain'}
current_country_slug = country_slugs[I18n.locale]
#country = Country.find_by_slug(current_country_slug)
end
And now I can get cities in my controller only for current country:
def index
#cities = #country.cities
#starred_cities = #cities.where(starred: true)
end
Now I have some trouble because my controller test fails with exception:
Failures:
1) CitiesController GET #index populates an array of all cities
Failure/Error: #cities = #country.cities
NoMethodError:
undefined method `cities' for nil:NilClass
# ./app/controllers/cities_controller.rb:5:in `index'
# ./spec/controllers/cities_controller_spec.rb:9:in `block (3 levels) in <top (required)>'
2) CitiesController GET #index renders index view
Failure/Error: #cities = #country.cities
NoMethodError:
undefined method `cities' for nil:NilClass
# ./app/controllers/cities_controller.rb:5:in `index'
# ./spec/controllers/cities_controller_spec.rb:9:in `block (3 levels) in <top (required)>'
Please help, what should I do to combine such instance variable and make an association on it?

Answer 1

You have to set up all associations used in the testcase properly, in your case the country with assigned cities is missing (thus nil.cities is called) or mock the methods to return the objects as AR would return them, like:
RSpec.describe CitiesController, :type => :controller do
describe '#index' do
let(:cities) { double('cities') }
let(:starred_cities) { double('starred_cities') }
let(:country) { double('country', cities: cities) }
before do
allow(cities).to receive(:where).with(starred: true).and_return(starred_cities)
allow(Country).to receive(:find_by_slug).and_return(country)
get :index
end
it 'populates an array of all cities' do
expect(assigns(:cities)).to match_array(cities)
end
it 'renders index view' do
expect(response).to render_template :index
end
end
end
Mocking can be quite usefull if you know what you are doing to prevent hitting the db (slow!) since AR is already quite tested well. But also can let you write passing tests although your implementation has bugs, so use it wisely.