Add spec for failing Paypal checkout
user
```ruby
require "spec_helper"

feature "Checking out with Paypal", js: true do
  include ShopWorkflow
  include CheckoutWorkflow

  let(:distributor) { create(:distributor_enterprise) }
  let(:supplier) { create(:supplier_enterprise) }
  let(:product) { create(:simple_product, supplier: supplier) }
  let(:variant) { product.variants.first }
  let(:order_cycle) {
    create(
      :simple_order_cycle,
      suppliers: [supplier],
      distributors: [distributor],
      coordinator: distributor,
      variants: [variant]
    )
  }
  let(:order) {
    create(
      :order,
      order_cycle: order_cycle,
      distributor: distributor,
      bill_address_id: nil,
      ship_address_id: nil
    )
  }
  let(:free_shipping) { create(:shipping_method) }
  let!(:paypal) do
    Spree::Gateway::PayPalExpress.create!(
      name: "Paypal",
      environment: "test",
      distributor_ids: [distributor.id]
    )
  end

  before do
    distributor.shipping_methods << free_shipping
    set_order order
    add_product_to_cart order, product
  end

  describe "as a guest" do
    it "fails with an error message" do
      pending "The checkout_state_path is missing."

      visit checkout_path
      complete_the_form

      paypal_response = double(:response, success?: false, errors: [])
      paypal_provider = double(
        :provider,
        build_set_express_checkout: nil,
        set_express_checkout: paypal_response
      )
      allow_any_instance_of(Spree::PaypalController).to receive(:provider).
        and_return(paypal_provider)

      place_order
      expect(page).to have_content "PayPal failed."
    end
  end

  def complete_the_form
    checkout_as_guest

    within "#details" do
      fill_in "First Name", with: "Will"
      fill_in "Last Name", with: "Marshall"
      fill_in "Email", with: "test@test.com"
      fill_in "Phone", with: "0468363090"
    end

    within "#billing" do
      fill_in "City", with: "Melbourne"
      fill_in "Postcode", with: "3066"
      fill_in "Address", with: "123 Your Head"
      select "Australia", from: "Country"
      select "Victoria", from: "State"
    end

    within "#shipping" do
      choose free_shipping.name
    end
    within "#payment" do
      choose paypal.name
    end
  end
end
```
assistant