Python assertEqual

Summary: in this tutorial, you’ll learn how to use the Python assertEqual() method to test if two values are equal.

Introduction to the Python assertEqual() method #

The assertEqual() is a method of the TestCase class of the unittest module. The assertEqual() tests if two values are equal:

assertEqual(first, second, msg=None)Copy

If the first value does not equal the second value, the test will fail.

The msg is optional. If the msg is provided, it’ll be shown on the test result if the test fails.

Python assertEqual() method example #

First, create a new module called main.py and define the add() function:

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

Second, create a test module test_main.py to test the add() function:

import unittest

from main import add


class TestMain(unittest.TestCase):
    def test_add(self):
        self.assertEqual(add(1, 2), 3)Copy

Third, run the test:

python -m unittest test_main.py -vCopy

Output:

test_add (test_main.TestMain) ... ok

----------------------------------------------------------------------
Ran 1 test in 0.000s

OKCopy

Python assertNotEqual() method #

The assertNotEqual() method tests if two values are not equal:

assertNotEqual(first, second, msg=None)Copy

If the first is equal to the second, the test will fail. Otherwise, it’ll pass. For example:

import unittest

from main import add


class TestMain(unittest.TestCase):
    def test_add(self):
        self.assertEqual(add(1, 2), 3)

    def test_add_floats(self):
        self.assertNotEqual(add(0.2, 0.1), 0.3)Copy

Run the test:

python -m unittest test_main.py -vCopy

Output:

test_add (test_main.TestMain) ... ok
test_add_floats (test_main.TestMain) ... ok

----------------------------------------------------------------------
Ran 2 tests in 0.001s

OKCopy

Since 0.2 + 0.1 returns 0.30000000000000004, it’s not equal to 0.3. Therefore, the following test passes:

self.assertNotEqual(add(0.2, 0.1), 0.3)Copy

Summary #

• Use the assertEqual() method to test if two values are equal.
• Use the assertNotEqual() method to test if two values are not equal.