There are many test runners available for Python. The one built into the Python standard library is called unittest. In this tutorial, you will be using unittest test cases and the unittest test runner. The principles of unittest are easily portable to other frameworks. The three most popular test runners are:

• unittest
• nose or nose2
• pytest Choosing the best test runner for your requirements and level of experience is important.

unittest

unittest has been built into the Python standard library since version 2.1. You’ll probably see it in commercial Python applications and open-source projects.

unittest contains both a testing framework and a test runner.

unittest has some important requirements for writing and executing tests. unittest requires that:

• You put your tests into classes as methods
• You use a series of special assertion methods in the unittest.TestCase class instead of the built-in assert statement

To convert the earlier example to a unittest test case, you would have to:

1. Import unittest from the standard library
2. Create a class called TestSum that inherits from the TestCase class
3. Convert the test functions into methods by adding self as the first argument
4. Change the assertions to use the self.assertEqual() method on the TestCase class
5. Change the command-line entry point to call unittest.main()

Follow those steps by creating a new file test_sum_unittest.py with the following code:

import unittest


class TestSum(unittest.TestCase):

    def test_sum(self):
        self.assertEqual(sum([1, 2, 3]), 6, "Should be 6")

    def test_sum_tuple(self):
        self.assertEqual(sum((1, 2, 2)), 6, "Should be 6")

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

If you execute this at the command line, you’ll see one success (indicated with .) and one failure (indicated with F):

$ python test_sum_unittest.py
.F
======================================================================
FAIL: test_sum_tuple (__main__.TestSum)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "test_sum_unittest.py", line 9, in test_sum_tuple
    self.assertEqual(sum((1, 2, 2)), 6, "Should be 6")
AssertionError: Should be 6

----------------------------------------------------------------------
Ran 2 tests in 0.001s

FAILED (failures=1)

You have just executed two tests using the unittest test runner. For more information on unittest, you can explore the unittest Documentation.

pytest

pytest supports execution of unittest test cases. The real advantage of pytest comes by writing pytest test cases. pytest test cases are a series of functions in a Python file starting with the name test_.

pytest has some other great features:

• Support for the built-in assert statement instead of using special self.assert*() methods
• Support for filtering for test cases
• Ability to rerun from the last failing test
• An ecosystem of hundreds of plugins to extend the functionality

Writing the TestSum test case example for pytest would look like this:

def test_sum():
    assert sum([1, 2, 3]) == 6, "Should be 6"

def test_sum_tuple():
    assert sum((1, 2, 2)) == 6, "Should be 6"

You have dropped the TestCase, any use of classes, and the command-line entry point.

More information can be found at the Pytest Documentation Website.

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From realpython.com