rspec: mocking a reference to a polymorphic model?

rubyonrails-talk
1

The basic question: how do you mock (or stub) a reference to a polymorphic class in RSpec? Trying the obvious thing leads to an error of the form:

   undefined method `base_class' for Post:Class

=== The details:

# file: app/models/relation.rb class Relation < ActiveRecord::Base   belongs_to :entity, :polymorphic => true end

# file: db/xxx_create_relations.rb class CreateRelations < ActiveRecord::Migration   def change     create_table :relations do |t|       t.references :entity, :polymorphic => true, :null => false     end   end end

# file: spec/models/relation_spec.rb describe Relation do   it 'should create instance without error' do     post = mock_model("Post")     lambda { Relation.create!(:entity => @post)}.should_not raise_error   end end

=== Running the test:

  1) Relation should create instance without error      Failure/Error: lambda { Relation.create!(:entity => post) }.should_not raise_error        expected no Exception, got #<NoMethodError: undefined method `base_class' for Post:Class>      # ./spec/models/relation_spec.rb:39:in `block (2 levels) in <top (required)>'

My hunch is that ActiveRecord is calling base_class on the mocked model (Post) to determine what to stick in the 'entity_type' column in the relations table. I tried explicitly setting it, as in:

    post = mock_model("Post", :base_class => "Post")

but the error was the same.

For all the reasons that DC espouses, I'd love to mock (or stub) references to the polymorphic models, but I don't see how to do that. Any ideas?

2

I don't espouse stubbing or mocking associations, as it requires knowledge of Rails internals (as in your example). I do espouse stubbing domain-specific APIs on models in controller specs, because that provides fine-grained control of state and decoupling from the database, but that is an entirely different matter/context.

HTH, David