Test ActiveModel::Serializer classes with Rspec

Given the following ActiveModel::Serializer class:

class SampleSerializer < ActiveModel::Serializer
  attributes :id, :name
end

How can this be tested with RSpec?

Assumptions

This answer assumes you have the rspec-rails, active_model_serializers and factory_girl_rails gems installed and configured.

This answer also assumes you have defined a factory for the Sample resource.

Serializer spec

For the current version(0.10.0.rc3) of active_model_serializers at the time of writing, ActiveModel::Serializer classes do not receive to_json and are , instead, wrapped in an adapter class. To obtain the serialization of a model wrapped in a serializer instance, an instance of an adapter must be created:

before(:each) do
  # Create an instance of the model
  @sample = FactoryGirl.build(:sample)

  # Create a serializer instance
  @serializer = SampleSerializer.new(@sample)

  # Create a serialization based on the configured adapter
  @serialization = ActiveModelSerializers::Adapter.create(@serializer)
end

The adapter instance receives the to_json method and returns the serialization of the model.

subject { JSON.parse(@serialization.to_json) }

Expectations can then be run on the JSON returned.

it 'should have a name that matches' do
  expect(subject['name']).to eql(@sample.name)
end

When parsing the JSON response, the adapter configuration must be taken into consideration:

• The default config, :attributes, generates a JSON response without a root key:

  subject { JSON.parse(@serialization.to_json) }
  

• The :json config generates a JSON response with a root key based on the model's name:

  subject { JSON.parse(@serialization.to_json)['sample'] }
  

• The :json_api config generates a JSON that conforms to the jsonapi standard:

  subject { JSON.parse(@serialization.to_json)['data']['attributes'] }