Python CGI FieldStorage test harness

Question

How can I set up a small test harness for Python CGI script? I don't want to run a server in order to test it, but I do want to supply various GET/POST inputs for my test.

It appears to me that FieldStorage (or the object behind it) is utterly immutable, so I don't see how to supply the CGI data on the fly in a harness.

Answer 1

You could use a mocking library, such as Mock to do the job. For example, suppose you want to test the function_to_test function from your CGI script, you could write a unittest class like this:

import unittest
import cgi

from mock import patch

def function_to_test():
    form = cgi.FieldStorage()
    if "name" not in form or "addr" not in form:
        return "<H1>Error</H1>\nPlease fill in the name and address.\n"
    text = "<p>name: {0}\n<p>addr: {1}\n"
    return text.format(form["name"].value, form["addr"].value)

@patch('cgi.FieldStorage')
class TestClass(unittest.TestCase):
    class TestField(object):
        def __init__(self, value):
            self.value = value

    FIELDS = { "name" : TestField("Bill"), "addr" : TestField("1 Two Street") }

    def test_cgi(self, MockClass):
        instance = MockClass.return_value
        instance.__getitem__ = lambda s, key: TestClass.FIELDS[key]
        instance.__contains__ = lambda s, key: key in TestClass.FIELDS
        text = function_to_test()
        self.assertEqual(text, "<p>name: Bill\n<p>addr: 1 Two Street\n")

    def test_err(self, MockClass):
        instance = MockClass.return_value
        instance.__contains__ = lambda self, key: False
        text = function_to_test()
        self.assertEqual(text,
            "<H1>Error</H1>\nPlease fill in the name and address.\n")

If I run this code as a unit test I get:

..
----------------------------------------------------------------------
Ran 2 tests in 0.003s

OK