Unit test for the 'none' type in Python

Question

How would I go about testing for a function that does not return anything?

For example, say I have this function:

def is_in(char):     my_list = []     my_list.append(char) 

and then if I were to test it:

class TestIsIn(unittest.TestCase):      def test_one(self):     ''' Test if one character was added to the list'''     self.assertEqual(self.is_in('a'), # And this is where I am lost) 

I don't know what to assert the function is equal to, since there isn't any return value that I could compare it to.

Would assertIn work?

Answer 1

All Python functions return something. If you don't specify a return value, None is returned. So if your goal really is to make sure that something doesn't return a value, you can just say

self.assertIsNone(self.is_in('a')) 

(However, this can't distinguish between a function without an explicit return value and one which does return None.)

Answer 2

The point of a unit test is to test something that the function does. If it's not returning a value, then what is it actually doing? In this case, it doesn't appear to be doing anything, since my_list is a local variable, but if your function actually looked something like this:

def is_in(char, my_list):     my_list.append(char) 

Then you would want to test if char is actually appended to the list. Your test would be:

def test_one(self):     my_list = []     is_in('a', my_list)     self.assertEqual(my_list, ['a']) 

Since the function does not return a value, there isn't any point testing for it (unless you need make sure that it doesn't return a value).