unittest is a built-in testing framework for Python.

Getting Started

Create a new file in the same folder as your program called filename.test.py. Import unittest as well as the main program in the test file.

import unittest
import my_program

Once you have these, you can create test cases and unit tests within them. The test cases are subclasses of unittest.TestCase, and the unit tests need to be named test_ followed by whatever naming you want to use. Any method that does not start with test_ will not be run.

setUp and tearDown run at the beginning and end of each unit test. setUpClass and tearDownClass run at the beginning and end of each test case.

class WidgetTestCase(unittest.TestCase):
    def setUpClass()

    def setUp(self):
        self.widget = Widget('The widget')

    def tearDown(self):

    def test_default_widget_size(self):
        self.assertEqual(self.widget.size(), (50,50),
                         'incorrect default size')

    # You can disable tests by using this decorator
    @unittest.skip("reason for skipping") # reason is not necessary
    def test_widget_resize(self):
        self.assertEqual(self.widget.size(), (100,150),
                         'wrong size after resize')

You can run your test suite by running python3 -m unittest in the root directory of the program. This will search for files using unittest within the current directory.

Useful Assert Types

Assertion Description
assertRaises(Exception, function, *args, **kwargs) Assert that Exception gets raised when function is run with *args and **kwargs[6].

Run Part Of Test Suite

To run only certain classes, you can pass them at the end of the python3 call:

python3 -m unittest filename.WidgetTestCase

Mocking Input

To mock a call to input, you can utilize mock in the unittest library. The patch decorator allows you to specify a default return.[4]

import unittest
from unittest.mock import patch

def answer(input=input):
    ans = input('enter yes or no')
    if ans == 'yes':
        return 'you entered yes'
    if ans == 'no':
        return 'you entered no'

class Test(unittest.TestCase):
    # get_input will return 'yes' during this test
    @patch('builtins.input', return_value='yes')
    def test_answer_yes(self, input):
        self.assertEqual(answer(input=input), 'you entered yes')

    @patch('builtins.input', return_value='no')
    def test_answer_no(self, input):
        self.assertEqual(answer(input=input), 'you entered no')


  1. https://docs.python.org/3/library/unittest.html
  2. https://docs.python.org/3/library/unittest.html#skipping-tests-and-expected-failures
  3. https://stackoverflow.com/questions/2066508/disable-individual-python-unit-tests-temporarily
  4. https://stackoverflow.com/questions/21046717/python-mocking-raw-input-in-unittests
  5. https://stackoverflow.com/questions/1068246/python-unittest-how-to-run-only-part-of-a-test-file
  6. https://docs.python.org/3/library/unittest.html#unittest.TestCase.assertRaises

Last modified: 202209241453