new_contents: from rapidsms.router import Router
  
  # a subclass of Router with all the moving parts replaced
  class MockRouter (Router):
      def __init__ (self):
          Router.__init__(self)
          self.logged = [] 
  
      def log(self, *args):
          self.logged.append(args)
      
      def add_backend (self, backend):
          self.backends.append(backend)
  
      def add_app (self, app):
          self.apps.append(app)
  
      def start (self):
          self.running = True
          self.start_all_backends()
          self.start_all_apps()
  
      def stop (self):
          self.running = False
          self.stop_all_backends()
  
subject: Add harness module with MockRouter class. We'll put MockBackend here, too.