Rspec for polymorphic classes

Rspec forum has troubles

Does anyone have examples for rspec model for a polymorphic class?

Since attributes get dynamically created into the db, this is different
to test than normal rspec models.

Factory Girl would be great too! Just a simple one will do!

I woiuld like to test the derived class (not the polymorphic class).

I am not sure I understand what you need, can you shows us your classes? It will be easier to answer your question if you give us your code maybe in a gist?

class Address < ActiveRecord::Base
    belongs_to :addressable, polymorphic: true

My Second Model: app/models/user.rb

class User < ActiveRecord::Base
    has_many :addresses, as: :addressable

My third model: app/models/company.rb

class Company < ActiveRecord::Base
     has_many :addresses, as: :addressable

For Address table, I have this migration:

class CreateAddresses < ActiveRecord::Migration
    def change
        create_table :addresses do |t|
            t.string :description
            t.references :addressable, polymorphic: true

I'm not sure why you can't write a normal rspec against these objects--- generally rspec tests the objects themselves and how their public methods are implemented (and, when appropriate, the internals of the object implementation).

The decision to make the attachment polymorphic -- which incidentally looks like a fine choice in this case -- is an implementation decision.

In these cases, I would test
• That a User can have many (add/remove) addresses
• That a Company can have many (add/remove) addresses)
• That an address that belongs to a User can be correctly instantiated (and addressable is the user you are expecting)
• That an address that belongs to a Company can be correctly instantiated (and addressable is the company you are expecting)

(Some might argue that the things I listed above are over-kill testing, since all you're really doing is testing active record. I generally do write a few of these style of tests for sanity, but tend to not go overboard testing every feature of the association interface --- those features provided by AR itself --- in my unit tests)

Remember, your rspec will say something like

address.addressable.should eq(user)

The decision to implement as polymorphic is an implementation decision, so although in your case addressable is a belong_to polymorphic association, it could easily be implemented as a method on the object itself. Your unit test should be abstract from that, making your implementation de-coupled from your test expectation.