ActionController::UnknownFormat - Capybara spec and AJAX requests - ruby-on-rails

Question

I got problem with my Capybara test. When I run spec with Selenium support (js: true) it goes through the instructions until it encounters click_on method, which hits create controller action and returns error message: "ActionController::UnknownFormat at /category/items
ActionController::UnknownFormat", which is probably respond_with(#items) issue. In fact, create method works fine as well as whole functionality on the server, but into test it crashes. What is more, item creates in the database, so that confirms create method works properly.
Request information:
GET No GET data
POST commit "Do AJAX request"
item {"item_id"=>"12345"}
utf8 "✓"
COOKIES cookie_policy "accepted"
Spec:
require 'spec_helper'
feature "Test in Capybara and Selenium", js: true do
background(:all) do
...seed data
end
scenario "my test scenario" do
visit root_path
visit '/category/1'
within first(".css_style") do
click_on("item_link")
end
# we are into item view
click_on("Do AJAX request") # error
visit another_view_path
end
end
Controller:
class ...::ItemsController < ...::BaseController
respond_to :html, except: ['create', ...]
respond_to :js, only: ['create', ...]
def create
...
#item.save
respond_with(#item)
end
Views:
thing view:
<%= link_to("request", category_items_path(item: {thing_id: thing}), method: :post, class: 'add_item_button', remote: true, name: "animate_item") %>
create.js.erb:
if($('#add-item-button').length > 0){
location.reload(200);
}
spec_helper.rb
...
require 'rspec/rails'
require 'rspec/autorun'
require 'capybara/rspec'
require 'capybara/rails'
require 'selenium-webdriver'
require 'rack/utils'
Capybara.app = Rack::ShowExceptions.new(Sklep::Application)
Capybara.register_driver :selenium do |app|
Capybara::Selenium::Driver.new(app, :browser => :chrome)
end
Capybara.default_driver = :selenium
...
If I forgot about something please let me know.