testing.md

Python by Example: Testing

Tests verify that your code works. The unittest module is built in: create a class that inherits from TestCase, write methods named test_*, and use assertions. Run tests with python -m unittest or python script.py. For larger projects, consider pytest, which has a simpler syntax.

What you'll learn:

• Writing test methods with test_ prefix
• Assertions: assertEqual, assertTrue, assertRaises
• Running tests

import unittest


def add(a, b):
    return a + b


class TestAdd(unittest.TestCase):
    def test_add_positive(self):
        self.assertEqual(add(2, 3), 5)

    def test_add_negative(self):
        self.assertEqual(add(-1, -1), -2)

    def test_add_zero(self):
        self.assertEqual(add(0, 0), 0)


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

assertEqual(a, b) checks that a == b. Use self.assertRaises(ValueError, func, arg) to test that a function raises. The if __name__ == "__main__" block lets you run tests with python testing.py.

To run this program:

$ python source/testing.py
...
----------------------------------------------------------------------
Ran 3 tests in 0.000s

OK

Tip: Run with python -m unittest discover to find and run all tests in a project.

Try it: Add a test for add(1.5, 2.5) and verify it returns 4.0.

Source: testing.py

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