meet it

runs every test in a and reports back.

A checks one small piece of code. The unittest module keeps them organised: write a test case, a child class of unittest.TestCase, with one method per test. Each method name must start with test_.

Your test case inherits checking methods. checks two values match, and with self.assertRaises(ValueError): checks that the lines inside it raise that error.

unittest.main(argv=["x"], exit=False) runs every test_ method. A dot means passed, an F means failed, and the last line says OK when everything passes.

import unittest
def discount(price, percent):
    return price - price * percent / 100
class TestDiscount(unittest.TestCase):
    def test_half_price(self):
        self.assertEqual(discount(40, 50), 20)
    def test_no_discount(self):
        self.assertEqual(discount(40, 0), 40)
unittest.main(argv=["x"], exit=False)

argv=["x"] stops unittest reading settings meant for something else, and exit=False lets your program carry on afterwards.

guess first

Run one test by hand. What will this show?

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

import unittest
class TestMaths(unittest.TestCase):
    def test_divide(self):
        self.assertEqual(10 / 2, 5)
        print("First check passed")
        self.assertEqual(10 / 4, 2)
        print("Second check passed")
TestMaths().test_divide()

your turn

Your turn. Test a halving function.

Fill in the method that checks two values are equal, and give it a number and its half. Then fill in the error that halving text should raise. Look for OK on the last line.

Your code

press run to see what happens

fix it

A test has found a bug. Fix the code, not the test!

Broken code to fix

press run to see what happens

One test passes and one fails. Read the failure: which two numbers did assertEqual compare?
The function always divides by 2, which only works for two numbers. An average divides by how many numbers there are.
Change / 2 to / len(numbers) on line 3, then run.

nailed it

you test like a professional. :D

A test case is a child class of unittest.TestCase.
unittest.main runs every method whose name starts with test_.
assertEqual and assertRaises report failures instead of crashing.

new words in your collection

unit test
unittest
test case
assertEqual

This lesson isn’t saved. A free account remembers every lesson you finish.

unittest runs every test in a test case and reports back.

Run one test by hand. What will this show?

Your turn. Test a halving function.

A test has found a bug. Fix the code, not the test!

you test like a professional. :D

runs every test in a and reports back.