• unittest
• TestCase
• assertEqual

Python comes with a built-in module for writing tests. Its name is unittest which might be a bit confusing as this module can be used to any kind of more complex feature-tests and other modules can be also used to write so called unit-tests.

Unlike the doctests that were part of the actual code, the unittest library calls for separate test files. It is recommended that the names of files start with the test_ prefix as that will make it easy for the various testing tools to locate them.

Inside the file you'd need to import both the unittest module and the module that we are testing. mystest in this case.

We need a class with a name that starts with Test and inherits from unittest.TestCase. In the class we can have one or more testing functions. Each one starts with a test_ prefix. Inside the function we can call the function that we are testing and we can compare the result returned by it to some expected value. We can compare them in various ways using the various assert-methods of the unittest.TestCase. In this example we used the assertEqual method as we wanted to make sure the actual return value equals the expected value.

We can run the tests using python -m unittest test_one_with_unittest.py. It will have some output on the screen indicating all the tests passed. The exit-code will be 0 as expected.

import unittest
import mymath

class TestMath(unittest.TestCase):
    def test_math(self):
        self.assertEqual(mymath.add(2, 2), 4)

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

OK

$ python -m unittest test_one_with_unittest.py
$ echo $?
0

> python -m unittest test_one_with_unittest.py
> echo %ERRORLEVEL%
0