How to Stub Non-ActiveRecord Models in Rails?

Question

I have a model like this:

class Thing
  class << self
    def do_stuff(param)
      result1 = method_one(param)   
      result2 = method_two(result1)
    end

    def method_one(param)
      # tranformation
    end 

    def method_two(result1)
      # transformation
    end
  end
end

How can I test that do_stuff is properly executing the methods of method_one and method_two with the right arguments? I have tried mock_model / mock_class but those don't make any sense to me. I have read the documentation but I'm still having a hard time making sense of it.

My test looks like this:

require 'rails_helper'

RSpec.describe Thing, type: :model do
  let!(:param) { create(:param) }

  describe '#do_stuff' do
    thing = double('thing')
    expect(thing).to receive(:method_one).with param
    thing.do_stuff param
  end
end

Why does this not work? The error I receive is that thing received an unexpected message param. But it was quite expected and that was the test. Where am I going wrong?

Answer 1

I think you shouldn't double your model. Following example works for me:

class Thing
  class << self
    def do_stuff(param)
      result1 = method_one(param)
      result2 = method_two(result1)
    end

    def method_one(param)
      param[:foo]
    end

    def method_two(result1)
      # transformation
      result1
    end
  end
end

# thing_spec.rb
require 'rails_helper'

RSpec.describe Thing, type: :model do
  let!(:param) { {foo: "bar"} }

  describe '#do_stuff' do
    it 'should do stuff' do
      expect(Thing).to receive(:method_one).with(param)
      Thing.do_stuff param
    end
  end
end

Test result

[retgoat@iMac-Roman ~/workspace/tapp]$ be rspec spec/models/thing_spec.rb
DEPRECATION WARNING: The configuration option `config.serve_static_assets` has been renamed to `config.serve_static_files` to clarify its role (it merely enables serving everything in the `public` folder and is unrelated to the asset pipeline). The `serve_static_assets` alias will be removed in Rails 5.0. Please migrate your configuration files accordingly. (called from block in <top (required)> at /Users/retgoat/workspace/tapp/config/environments/test.rb:16)
.

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