[rails] RSpec render_layout expects render specified layout file

Original idea via http://rubyforge.org/pipermail/rspec-users/2007-October/004026.html

Add some code into your spec/spec_helper.rb is as follows:

class RenderLayout
  def initialize(expected)
    @expected = 'layouts/' + expected
  end

  def matches?(controller)
    @actual = controller.layout
    @actual == @expected
  end

  def failure_message
    return "render_layout expected #{@expected.inspect}, got #{@actual.inspect}", @expected, @acutual
  end

  def negative_failure_message
    return "render_layout expected #{@expected.inspect} not to equal #{@actual.inspect}", @expected, @actual
  end
end

def render_layout(expected)
  RenderLayout.new(expected)
end

your_controller_spec.rb

it "should render 'application' layout file" do
   get :index
   response.should render_layout('application')
end