[rails]Spork中出现“Could not start Spork server for RSpec”的解决方案

16:59:14 - INFO - Starting Spork for RSpec, Test::Unit
Couldn't find a supported test framework that begins with 'testunit'

Supported test frameworks:
( ) Cucumber
(*) RSpec

Legend: ( ) - not detected in project   (*) - detected
Using RSpec, Rails
Preloading Rails environment
Loading Spork.prefork block...
Spork is ready and listening on 8989!
16:59:44 - ERROR - Could not start Spork server for RSpec, Test::Unit after 30 seconds. I will continue waiting for a further 60 seconds.