module Shoulda::ActionController::Matchers

def render_with_layout(layout = nil)

it { should_not render_with_layout }
it { should render_with_layout(:special) }
it { should render_with_layout }

Example:

Ensures that the controller rendered with the given layout. 
def render_with_layout(layout = nil)
  RenderWithLayout.new(layout)
end