http://code.google.com/p/wsgi-intercept/

Testing a WSGI application normally involves starting a server at a local host and port, then pointing your test code to that address. Instead, this library lets you intercept calls to any specific host/port combination and redirect them into a WSGI application importable by your test program. Thus, you can avoid spawning multiple processes or threads to test your Web app.
How Does It Work?

wsgi_intercept works by replacing httplib.HTTPConnection with a subclass, wsgi_intercept.WSGI_HTTPConnection. This class then redirects specific server/port combinations into a WSGI application by emulating a socket. If no intercept is registered for the host and port requested, those requests are passed on to the standard handler.

The functions add_wsgi_intercept(host, port, app_create_fn, script_name='') and remove_wsgi_intercept(host,port) specify which URLs should be redirect into what applications. Note especially that app_create_fn is a function object returning a WSGI application; script_name becomes SCRIPT_NAME in the WSGI app's environment, if set.