python function help

[ndc85430]

Personally, I prefer to get the computer to do the work of checking the results. So, I write tests:

import unittest


class SubtractElementsTest(unittest.TestCase):
    def test_it_subtracts_all_the_elements_from_the_list(self):
        result = subtractElements([100, 20, 4, 10])

        self.assertEqual(result, 66)


if __name__ == '__main__':
    unittest.main()

Saving this in a file called test_subtract_elements.py and running it gives

Output:
$ python3 test_subtract_elements.py 
E
======================================================================
ERROR: test_it_subtracts_all_the_elements_from_the_list (__main__.SubtractElementsTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "test_subtract_elements.py", line 6, in test_it_subtracts_all_the_elements_from_the_list
    result = subtractElements([100, 20, 4, 10])
NameError: name 'subtractElements' is not defined

----------------------------------------------------------------------
Ran 1 test in 0.000s

FAILED (errors=1)

So now I can gradually make it work, using the tests for feedback.