how to unittest the template variables passed to jinja2 template from webapp2 request handler

You can mock BaseHandler.render_template method and test its parameters.

See this question for a list of popular Python mocking frameworks.

Thanks to proppy's suggestion I ended up using a mock.

http://www.voidspace.org.uk/python/mock/

(mock is included as part or unittest.mock in python 3)

So here is my main.py code which is similar to what I have in webapp2:

note instead of BaseHandler.render_template i have BaseHandler.say_yo

__author__ = 'Robert'

print "hello from main"

class BaseHandler():
    def say_yo(self,some_number=99):
        print "yo"
        return "sup"

class TheHandler(BaseHandler):
    def get(self, my_number=42):
        print "in TheHandler's get()"
        print self.say_yo(my_number)
        return "TheHandler's return string"

and atest.py:

__author__ = 'Robert'

import unittest
import main
from mock import patch

class DemoTestCase(unittest.TestCase):
    def setUp(self):
        pass

    def tearDown(self):
        pass

    def testNothing(self):
        self.assertEqual(42, 21 + 21)

    def testSomeRequests(self):
        print "hi"
        bh = main.BaseHandler()
        print bh.say_yo()

        print "1111111"

        with patch('main.BaseHandler.say_yo') as patched_bh:
            print dir(patched_bh)
            patched_bh.return_value = 'double_sup'
            bh2 = main.BaseHandler()
            print bh2.say_yo()
            print "222222"

        bh3 = main.BaseHandler()
        print bh3.say_yo()

        print "3333"

        th = main.TheHandler()
        print th.get()

        print "44444"
        with patch('main.BaseHandler.say_yo') as patched_bh:
            patched_bh.return_value = 'last_sup'
            th = main.TheHandler()
            print th.get()
            print th.get(123)
            print "---"
            print patched_bh.called
            print patched_bh.call_args_list
            print "555555"



if __name__ == '__main__':
    unittest.main()

this code gives lots of output, here is a sample:

44444
in TheHandler's get()
last_sup
TheHandler's return string
in TheHandler's get()
last_sup
TheHandler's return string
---
True
[call(42), call(123)]
555555