Modifying global variables in Python unittest framework

Question

I am working on a series of unit tests in Python, some of which depend on the value of a configuration variable. These variables are stored in a global Python config file and are used in other modules. I would like to write unit tests for different values of the configuration variables but have not yet found a way to do this.

I do not have the possibility to rewrite the signatures of the methods I'm testing.

This is what I would like to achieve:

from my_module import my_function_with_global_var

class TestSomething(self.unittest):

    def test_first_case(self):
         from config import MY_CONFIG_VARIABLE
         MY_CONFIG_VARIABLE = True
         self.assertEqual(my_function_with_global_var(), "First result")

    def test_second_case(self):
         from config import MY_CONFIG_VARIABLE
         MY_CONFIG_VARIABLE = False
         self.assertEqual(my_function_with_global_var(), "Second result")

Thanks.

Edit: Made the example code more explicite.

Answer 1

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")