Ruby on Rails

On Thu, Mar 22, 2012 at 7:23 AM, Fearless Fool <lists@ruby-forum.com> wrote:
> 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?

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

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