nil：NilClass的未定义方法“ env”

我将rspec从版本2升级到了3。之后，我遇到了这个问题：

Failures:

  1) AlbumsController GET #edit 
     Failure/Error: sign_in_and_switch_schema @user
     NoMethodError:
       undefined method `env' for nil:NilClass
     # ./spec/support/auth_helpers.rb:10:in `sign_in_and_switch_schema'
     # ./spec/controllers/albums_controller_spec.rb:12:in `block (2 levels) in <top (required)>'

spec_helper.rb包含：

 RSpec.configure do |config|
    # most omitted
    config.include Warden::Test::Helpers
    config.include Devise::TestHelpers, type: :controller
 end

albums_controller_spec.rb：

describe AlbumsController do

  let(:album) { create(:album) }

  before(:all) do
    @user = create :user
  end

  before(:each) do
    sign_in_and_switch_schema @user
  end

  after(:all) do
    destroy_users_schema @user
    destroy_user @user
  end

 # describe's part omitted
end

auth_helpers.rb发生错误的部分：

def sign_in_and_switch_schema(user)
 # binding.pry
 @request.env["devise.mapping"] = Devise.mappings[:user] # <- error line
 sign_in :user, user

 Apartment::Tenant.switch(user.username) 
end

我当时正在寻找另一个类似的问答，但没有任何帮助。让我知道我是否应该再增加一些内容。提前致谢。