RSpec matcher for grape-entity

represent_matcher.rb

# Alternative: https://github.com/agileanimal/grape-entity-matchers

RSpec::Matchers.define :represent do |expected|
  match do |actual|
    exposes? && aliases? && has_presenter? && has_runtime_exposure?
  end

  chain :as do |as_alias|
    @as_alias = as_alias
  end

  chain :using do |entity|
    @entity = entity
  end

  chain :exposes_at_runtime do |object, exposure|
    @transformation_object, @transformation_exposure = object, exposure
  end


  private

    def exposes?
      actual.exposures.key?(expected)
    end

    def aliases?
      actual.exposures[expected][:as] == @as_alias
    end

    def has_presenter?
      actual.exposures[expected][:using] == @entity
    end

    def has_runtime_exposure?
      if @transformation_object && @transformation_exposure
        actual.exposures[expected][:proc].call(@transformation_object) == @transformation_exposure
      else
        true
      end
    end
end

representation_spec.rb

# Entities

class Value
  expose :code
  expose :desc, as: :description
end

class Parameter
  expose :id do |parameter|
    parameter.id.to_s
  end
  
  expose :variable
  expose :desc, as: :description

  expose :values, using: Value
end


# Specs

RSpec.describe Value do
  subject { Value }

  it { is_expected.to represent(:code) }
  it { is_expected.to represent(:desc).as(:description) }
end

RSpec.describe Parameter do
  subject { Parameter }

  let(:parameter) { OpenStruct.new(id: UUIDTools::UUID.random_create) }
  
  # One-liner syntax (https://relishapp.com/rspec/rspec-core/docs/subject/one-liner-syntax)
  it { is_expected.to represent(:id).exposes_at_runtime(parameter, parameter.id.to_s) }
  it { is_expected.to represent(:variable) }
  it { is_expected.to represent(:desc).as(:description) }
  
  it 'expected to represent values' do
    expect(subject).to represent(:values).using(OnOff::API::Entities::Value)
  end
end