Testing — Verify Your Code Works

unittest (built-in):

import unittest

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

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

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

    def test_zero(self):
        self.assertEqual(add(0, 5), 5)

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

pytest (install: pip install pytest):

def test_add():
    assert add(2, 3) == 5

def test_add_negative():
    assert add(-1, -1) == -2

Run with: pytest test_file.py or just pytest

Common assertions (unittest):

assertEqual, assertNotEqual, assertTrue, assertFalse, assertIsNone, assertIn, assertRaises

Test-Driven Development (TDD): Write the test FIRST, then write the code to make it pass. Sounds counterintuitive, but catches design problems early.

Reference:

Wikipedia: Unit Testing

https://en.wikipedia.org/wiki/Unit_testing