UnitTesting the webapp.RequestHandler in GAE - Python

I'm struggling on how to setup my environment for TDD with Google App Engine - Python. (I'm also pretty new to Python). My environment is as follows:

• Google App Engine 1.5.0
• IntelliJ 10.2
• IntelliJ setup to use Python 2.5.4 for this project

I am using IntelliJ with the Python plugin, so running unittests is as simple as hitting ctrl-shft-f10.

I've also read the documentation on testbed and have successfully tested the datastore and memcache. However, where I am stuck is how do i unittest my RequestHandlers. I've scanned a lot of articles on Google and most of them seem to be pre merging of gaetestbed into gae as testbed.

In the following code sample, i would like to know how to write a unit test (which is runnable in intellij) which tests that a call to '/' returns -> Home Page

from google.appengine.ext import webapp
import wsgiref.handlers

class MainHandler(webapp.RequestHandler):

    def get(self):
        self.response.out.write('Home Page')

paths = [
          ('/', MainHandler)
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application = webapp.WSGIApplication(paths, debug=True)

def main():
    wsgiref.handlers.CGIHandler().run(application)

if __name__ == '__main__':
    main()

From Nick Johnson's answer below, I added a new folder named test and added a file to that folder called unit_test.py. To that file I added the following code (Modified from Kris' answer below):

from StringIO import StringIO
from main import MainHandler
import unittest
from google.appengine.ext import webapp

class MyTestCase(unittest.TestCase):
    def test_get(self):
        request = webapp.Request({
            "wsgi.input": StringIO(),
            "CONTENT_LENGTH": 0,
            "METHOD": "GET",
                            "PATH_INFO": "/",
        })
        response = webapp.Response()
        handler = MainHandler()
        handler.initialize(request, response)
        handler.get()
        self.assertEqual(response.out.getvalue(), "Home Page")

And it now works!

I found that I needed a slightly-modified version of Nick Johnson's code:

request = webapp.Request({
    "wsgi.input": StringIO.StringIO(),
    "CONTENT_LENGTH": 0,
    "METHOD": "GET",
    "PATH_INFO": "/",
})
response = webapp.Response()
handler = MainHandler()
handler.initialize(request, response)
handler.get()
self.assertEqual(response.out.getvalue(), "Home Page")

The easiest way to do this is to instantiate the handler and pass it request and response objects, then assert on the results:

request = webapp.Request({
    "wsgi.input": StringIO.StringIO(),
    "CONTENT_LENGTH": 0,
    "METHOD": "GET",
})
request.path = '/'
response = webapp.Response()
handler = MainHandler()
handler.initialize(request, response)
handler.get()
self.assertEqual(response.body, "Home Page")