Unit testing with unittest

A unit test checks one small piece of behavior automatically and reports pass or fail. A suite of fast, repeatable tests tells you quickly when a change breaks something. Tests also serve as executable documentation: they show how a function is expected to behave, including in unusual cases.

Python

import io
import unittest


def apply_discount(price_cents, percent):
    if not 0 <= percent <= 100:
        raise ValueError("percent must be between 0 and 100")
    return price_cents * (100 - percent) // 100


class DiscountTests(unittest.TestCase):
    def test_typical_discount(self):
        self.assertEqual(apply_discount(8000, 25), 6000)

    def test_zero_discount_keeps_price(self):
        self.assertEqual(apply_discount(1999, 0), 1999)

    def test_invalid_percent_is_rejected(self):
        with self.assertRaises(ValueError):
            apply_discount(1000, 120)


suite = unittest.defaultTestLoader.loadTestsFromTestCase(DiscountTests)
result = unittest.TextTestRunner(stream=io.StringIO()).run(suite)
print(result.testsRun, result.wasSuccessful())

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