Add specs for cdn:containers:add command set.
user
```ruby
require File.expand_path(File.dirname(__FILE__) + '/../../../spec_helper')

describe "cdn:containers:add command" do

  def cli
    @cli ||= HP::Cloud::CLI.new
  end

  before(:all) do
    @hp_svc = storage_connection
    @hp_cdn = cdn_connection
    begin
      purge_containers(@hp_svc)
    rescue
      # ignore errors
    end
  end

  context "putting an existing storage container on the CDN" do

    before(:all) do
      @hp_svc.put_container('my-added-container')
      @response, @exit = run_command('cdn:containers:add my-added-container').stdout_and_exit_status
    end

    it "should show success message" do
      @response.should eql("Added container 'my-added-container' to the CDN.\n")
    end
    its_exit_status_should_be(:success)

    it "should have added the container to the CDN" do
      @hp_cdn.head_container('my-added-container').status.should eql(204)
    end

    after(:all) do
      @hp_cdn.delete_container('my-added-container')
      @hp_svc.delete_container('my-added-container')
    end

  end

  context "putting a non-existent storage container on the CDN" do

    before(:all) do
      @response, @exit = run_command('cdn:containers:add not-a-container').stderr_and_exit_status
    end

    it "should show error message" do
      @response.should eql("The container 'not-a-container' does not exist in your storage account. Please create the storage container first and then add it to the CDN.\n")
    end
    its_exit_status_should_be(:incorrect_usage)

  end

end```
assistant