How to assign session value to instance variable in Rspec controller?

My rails code as follow:

我的rails代码如下:

class MyController < ApplicationController
  def index
    @session_is_admin = session[:user_permission][:is_admin]
    begin
      @obj = Class.all
      respond_to do |format|
        format.html # index.html.erb
      end
    rescue
    end
  end
end
class