Forum: RSpec received unexpected message :id= with (20)

Please help me to understand this error message:

 1) PostsController#create when logged in should create a new post and
redirect to a successful message page
     Failure/Error: post 'create', { post: {title: 'New post',
       Mock Post(id: integer, title: string, description: text,
location: string, created_at: datetime, updated_at: datetime, status:
string, tags: string, views: integer, user_id: integer) received
unexpected message :id= with (20)
     # ./spec/controllers/posts_controller_spec.rb:56:in `block (4
levels) in <top (required)>'

Finished in 0.59991 seconds
6 examples, 1 failure



I'm trying to figure out this for about a week or more :(