Substitution of request.formats: [“text/html”] with [“application/javascript”]

Question

That`s my carts_controller.rb. By default controller action add renders add.js.erb in /app/views/carts/

class CartsController < ApplicationController
  def add
    find_cart_and_product
    @cart.products << @product
    CartMailer.product_added(@product).deliver_now
  end
end

and my test

describe 'POST #add' do
  let(:cart_full_of){ create(:cart_with_products) }
  let(:product){ create(:product) }
  before do
    post :add, session: { cart_id: cart_full_of.id }, params: { product_id: product.id}
  end
  it { expect(response.status).to eq(200) }
  it { expect(response.headers["Content-Type"]).to eql("application/javascript"; charset=utf-8")}
  it { is_expected.to render_template :add }
  it 'should add current product into cart' do
    expect(cart_full_of.products).to eq([product])
  end
end

has failed with common error for all test items:

 Failure/Error: post :add, session: { cart_id: cart_full_of.id }, params: { product_id: product.id}

 ActionController::UnknownFormat:
   CartsController#add is missing a template for this request format and variant.

   request.formats: ["text/html"]
   request.variant: []

I consider problem with expected requesting format, so how to force tests render with request.formats: ["application/javascript"] instead ["text/html"]?

Answer 1

This works for me (Rspec 3):

before :each do
  request.headers["accept"] = 'application/javascript'
end