meet it

Good tests check one behaviour, including the edge cases.

A good test checks one behaviour and has a name that says which. Test the normal case, then hunt for an or two: empty lists, zero, negative numbers, missing keys. Bugs love the edges.

runs before every test, so each one starts fresh. passes only if the code inside raises that error. checks many inputs in one test and reports each failure separately.

import unittest
def average(scores):
    if len(scores) == 0:
        raise ValueError("no scores")
    return sum(scores) / len(scores)

class AverageTests(unittest.TestCase):
    def test_typical_scores(self):
        self.assertEqual(average([2, 4, 6]), 4)
    def test_empty_list_is_an_error(self):
        with self.assertRaises(ValueError):
            average([])

unittest.main(argv=["x"], exit=False)

The time on the Ran 2 tests line changes from run to run, so never test your tests by it.

guess first

Does each test get a fresh basket? What will this show?

Guess before you run it. Wrong guesses are how you learn, and nothing is marked.

import unittest

class BasketTests(unittest.TestCase):
    def setUp(self):
        self.items = ["tea"]
        print("setUp")
    def test_add(self):
        self.items.append("cake")
        print("add:", self.items)
    def test_fresh(self):
        print("fresh:", self.items)

suite = unittest.defaultTestLoader.loadTestsFromTestCase(BasketTests)
suite.run(unittest.TestResult())

your turn

Your turn. Test several totals in one go.

Add a third basket total, in pence, that should ship free. Then fill the second blank with the helper that reports each case on its own.

Your code

press run to see what happens

fix it

The error was expected, yet the test fails. Fix it!

Broken code to fix

press run to see what happens

The report says the ValueError escaped. Was parse_age called inside the check?
assertRaises on a line of its own checks nothing. It needs with, and the risky call indented under it.
Write with self.assertRaises(ValueError): and indent parse_age("-5") beneath it, then run.

nailed it

your tests catch bugs at the edges. :D

One behaviour per test, with a name that says which.
setUp gives every test fresh data.
assertRaises and subTest cover errors and many cases.

new words in your collection

edge case
setUp
assertRaises
subTest

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