| Module | ActionController::Integration::Runner | 
| In: | lib/action_controller/integration.rb | 
Open a new session instance. If a block is given, the new session is yielded to the block before being returned.
  session = open_session do |sess|
    sess.extend(CustomAssertions)
  end
By default, a single session is automatically created for you, but you can use this method to open multiple sessions that ought to be tested simultaneously.