34. Unit testing with unittest/assert

Python's built-in `assert` statement raises `AssertionError` if the condition is false, and is the simplest form of testing.

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

assert add(2, 3) == 5, "add(2, 3) should be 5"

The standard library's `unittest` module provides structured test classes:

python
import unittest

class TestAdd(unittest.TestCase):
    def test_basic(self):
        self.assertEqual(add(2, 3), 5)
        self.assertTrue(add(0, 0) == 0)

Good tests cover typical inputs, edge cases (zero, negative, empty), and expected failure modes.

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