Rails and Rspec - Has One Through Polymorphic -

i trying test has_one :through relationship in rails using shoulda matchers.

my relationship structure looks (it's reverse polymorphic association - https://gist.github.com/runemadsen/1242485 )

class container < activerecord::base   has_many :contents   has_many :videos, through: :contents, source: :item, source_type: "video" end  class content < activerecord::base   belongs_to :container, dependent: :destroy   belongs_to :item, polymorphic: true, dependent: :destroy end  class video < activerecord::base   has_one :content, as: :item   has_one :container, through: :contents end 

this shoulda matcher code in rspec:

# video_spec.rb { should have_one(:container).through(:contents) } 

the error is:

undefined method `klass' nil:nilclass 

can tell me why i'm receiving error , how test association?

assuming that's all code in spec file (i apologize if posted trimmed down version), need nest shoulda matcher under describe block video class:

describe video   { should have_one(:container).through(:contents) } end 

the error you're getting indicates subject under test nil. nesting spec inside describe block video class, subject under test implicitly video class.

take peak @ documentation in source code, has ton of examples in it.