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") 

Answer 2

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? .