thoughtbot--shoulda-matchers/lib/shoulda/matchers/action_controller/render_with_layout_matcher.rb

module Shoulda
  module Matchers
    module ActionController
      # The `render_with_layout` matcher asserts that an action is rendered with
      # a particular layout.
      #
      #     class PostsController < ApplicationController
      #       def show
      #         render layout: 'posts'
      #       end
      #     end
      #
      #     # RSpec
      #     RSpec.describe PostsController, type: :controller do
      #       describe 'GET #show' do
      #         before { get :show }
      #
      #         it { should render_with_layout('posts') }
      #       end
      #     end
      #
      #     # Minitest (Shoulda)
      #     class PostsControllerTest < ActionController::TestCase
      #       context 'GET #show' do
      #         setup { get :show }
      #
      #         should render_with_layout('posts')
      #       end
      #     end
      #
      # It can also be used to assert that the action is not rendered with a
      # layout at all:
      #
      #     class PostsController < ApplicationController
      #       def sidebar
      #         render layout: false
      #       end
      #     end
      #
      #     # RSpec
      #     RSpec.describe PostsController, type: :controller do
      #       describe 'GET #sidebar' do
      #         before { get :sidebar }
      #
      #         it { should_not render_with_layout }
      #       end
      #     end
      #
      #     # Minitest (Shoulda)
      #     class PostsControllerTest < ActionController::TestCase
      #       context 'GET #sidebar' do
      #         setup { get :sidebar }
      #
      #         should_not render_with_layout
      #       end
      #     end
      #
      # @return [RenderWithLayoutMatcher]
      #
      def render_with_layout(expected_layout = nil)
        RenderWithLayoutMatcher.new(expected_layout).in_context(self)
      end

      # @private
      class RenderWithLayoutMatcher
        def initialize(expected_layout)
          if expected_layout
            @expected_layout = expected_layout.to_s
          else
            @expected_layout = nil
          end

          @controller = nil
        end

        # Used to provide access to layouts recorded by
        # ActionController::TemplateAssertions in Rails 3
        def in_context(context)
          @context = context
          self
        end

        def matches?(controller)
          @controller = controller
          rendered_with_layout? && rendered_with_expected_layout?
        end

        def failure_message
          "Expected #{expectation}, but #{result}"
        end

        def failure_message_when_negated
          "Did not expect #{expectation}, but #{result}"
        end

        def description
          description = 'render with '
          if @expected_layout.nil?
            description << 'a layout'
          else
            description << "the #{@expected_layout.inspect} layout"
          end
          description
        end

        private

        def rendered_with_layout?
          !rendered_layouts.empty?
        end

        def rendered_with_expected_layout?
          if @expected_layout.nil?
            true
          else
            rendered_layouts.include?(@expected_layout)
          end
        end

        def rendered_layouts
          recorded_layouts.keys.compact.map { |layout| layout.sub(%r{^layouts/}, '') }
        end

        def recorded_layouts
          if @context
            @context.instance_variable_get('@_layouts')
          else
            {}
          end
        end

        def expectation
          "to #{description}"
        end

        def result
          if rendered_with_layout?
            'rendered with ' + rendered_layouts.map(&:inspect).join(', ')
          else
            'rendered without a layout'
          end
        end
      end
    end
  end
end