unit testing python how tos [closed]

Question

I am new to Github. I am new to writing Unit Test Cases. I have contributed to a project but the owner has asked me to provide unit testcases that fail before the fix and work after the fix. How can I go about doing it? Shall I write them all together? As at one time I will have one copy of the code (i.e with fix or without fix). I am using Python and importing unittest. I am confused. Before the fix I get an exception so should I use assertRaises() for that. I did read a lot but am not able to start.

Answer 1

Assume you have a fix for following broken delta function:

Broken version:

def delta(a, b):
    return a - b

Fixed version:

def delta(a, b):
    return abs(a - b)

Then, provide following testcase. It will fail with the broken version, and work with the fixed version.

import unittest

from module_you_fixed import delta

class TestDelta(unittest.TestCase):
    def test_delta(self):
        self.assertEqual(delta(9, 7), 2)
        self.assertEqual(delta(2, 5), 3)

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

I assumed the project use standard library unittest module. You should use the framework that the project use.