sign_in_spec.rb

describe 'backbone', js: true do
  it 'success auth' do
    visit new_user_registration_path
    click_link 'Войдите'
    fill_backbone_field '#auth .sign-in #user_email', user.email
    fill_backbone_field '#auth .sign-in #user_password', user.password
    page.evaluate_script "$('#auth .sign-in .submit').trigger('click')"

    # shows flash
    page.should have_selector '.flash.success'
    # authorized
    page.should have_content "Личный кабинет"
    # stays on the same page
    current_path.should eq path
  end
end

/spec/support/feature_helpers.rb

def fill_backbone_field(selector, value)
  page.should have_selector selector
  page.evaluate_script "$('#{selector}').focus().val('#{value}').blur()"
end

spec_helper.rb

require 'capybara/poltergeist'
Capybara.register_driver :poltergeist_with_long_timeout do |app|
  Capybara::Poltergeist::Driver.new(app, timeout: 60)
end
Capybara.javascript_driver = :poltergeist_with_long_timeout