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

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

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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? .