Modifying global variables in Python unittest framework

You probably want to mock those global variables instead. The advantage of this is that the globals get reset once you're done. Python ships with a mocking module that lets you do this.

unittest.mock.patch be used as a decorator:

class TestSomething(self.unittest):    @patch('config.MY_CONFIG_VARIABLE', True)    def test_first_case(self):         self.assertEqual(my_function_with_global_var(), "First result")

You can also use it as a context manager:

    def test_first_case(self):        with patch('config.MY_CONFIG_VARIABLE', True):            self.assertEqual(my_function_with_global_var(), "First result")

Use unittest.mock.patch as in @Flimm's answer, if that's available to you.

Original Answer

Don't do this:

from my_module import my_function_with_global_var

But this:

import my_module

And then you can inject MY_CONFIG_VARIABLE into the imported my_module, without changing the system under test like so:

class TestSomething(unittest.TestCase): # Fixed that for you!    def test_first_case(self):         my_module.MY_CONFIG_VARIABLE = True         self.assertEqual(my_module.my_function_with_global_var(), "First result")    def test_second_case(self):         my_module.MY_CONFIG_VARIABLE = False         self.assertEqual(my_module.my_function_with_global_var(), "Second result")

I did something similar in my answer to How can I simulate input to stdin for pyunit? .

You code imports MY_CONFIG_VARIABLE into the local scope and then immediately overwrites the name with a different object. That won't change the value in the config module. Try

import configconfig.MY_CONFIG_VARIABLE = False

instead.