Как проверить действие входа в Facebook с Rails, Omniauth и Rspec

Я задал аналогичный вопрос раньше, но я думаю, что я прошел мимо моей первоначальной ошибки. Во всяком случае, у меня новая неудачная неудача, что у меня есть взрыв, пытающийся выяснить (обратите внимание на сарказм). Здесь мой отказ:

1) SessionsController#facebook_login should be valid
   Failure/Error: get :facebook_login
   NoMethodError:
     undefined method `slice' for nil:NilClass
   # ./app/models/user.rb:19:in `from_omniauth'
   # ./app/controllers/sessions_controller.rb:22:in `facebook_login'
   # ./spec/controllers/sessions_controller_spec.rb:96:in `block (3 levels) in <top (required)>'

sessions_controller_spec.rb

describe '#facebook_login' do

  before(:each) do
    valid_facebook_login_setup
    request.env["omniauth.auth"] = OmniAuth.config.mock_auth[:facebook]
    get :facebook_login
  end

  it "should be valid" do
    expect(response).to be_success
  end

  it "should set user_id" do
    expect(session[:user_id]).to be_true
  end
end

sessions_controller.rb

def facebook_login
  if request.env['omniauth.auth']
    user = User.from_omniauth(env['omniauth.auth'])
    session[:user_id] = user.id
    redirect_back_or root_path
  else
    redirect_to root_path
  end
end

omniauth_test_helper.rb

module OmniAuthTestHelper
  def valid_facebook_login_setup
    if Rails.env.test?
      OmniAuth.config.test_mode = true
      OmniAuth.config.mock_auth[:facebook] = OmniAuth::AuthHash.new({
        provider: 'facebook',
        uid: '123545',
        info: {
          first_name: "Andrea",
          last_name:  "Del Rio",
          email:      "[email protected]"
        },
        credentials: {
          token: "123456",
          expires_at: Time.now + 1.week
        }
      })
    end
  end

  def facebook_login_failure
    OmniAuth.config.mock_auth[:facebook] = :invalid_credentials
  end
end

spec_helper.rb

RSpec.configure do |config|
  config.include FactoryGirl::Syntax::Methods
  config.include Capybara::DSL
  config.fixture_path = "#{::Rails.root}/spec/fixtures"
  config.use_transactional_fixtures = true
  config.infer_base_class_for_anonymous_controllers = false
  config.order = "random"
  config.include SessionTestHelper, type: :controller
  config.include OmniAuthTestHelper, type: :controller
end

user.rb

class User < ActiveRecord::Base

  def self.from_omniauth(auth)
    where(auth.slice(:provider, :uid)).first_or_create do |user|
      user.provider = auth.provider
      user.uid = auth.uid
      user.first_name = auth.info.first_name
      user.last_name = auth.info.last_name
      user.email = auth.info.email
      user.password = auth.credentials.token
      user.password_confirmation = auth.credentials.token
      user.oauth_token = auth.credentials.token
      user.oauth_expires_at = Time.at(auth.credentials.expires_at)
    end
  end
end

Любая помощь будет действительно крутой. Спасибо, ребята!