Python unittest - unit test example

Published on August 3, 2022


Python unittest - unit test example

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Today we will learn about python unittest and look through python unit test example programs. In previous tutorial we learned about python zip function.

Python unittest

Python unittest module is used to test a unit of source code. Suppose, you need to test your project. You know what kind of data the function will return. After writing huge code, you need to check it whether the output is correct or not. Normally, what we do is printing the output and match it with the reference output file or check the output manually. To reduce this pain, Python has introduced unittest module. Using this module you can check the output of the function by some simple code. In this tutorial we will discuss about basic usage of Python unittest module and write some python unit test cases to test a class functions.

Python Unit Test Example Source

First of all we have to write some code to unit test them. We will have a Python class. The main purpose of the class is to store and retrieve person’s name. So, we write set_name() function to store the data and get_name() function to retrieve name from the class.

class Person:
    name = []

    def set_name(self, user_name):
        return len(self.name) - 1

    def get_name(self, user_id):
        if user_id >= len(self.name):
            return 'There is no such user'
            return self.name[user_id]

if __name__ == '__main__':
    person = Person()
    print('User Abbas has been added with id ', person.set_name('Abbas'))
    print('User associated with id 0 is ', person.get_name(0))

We named the class file as Person.py. And the output of the above code will be like below.

$ python3.6 Person.py 
User Abbas has been added with id  0
User associated with id 0 is  Abbas

Python unittest structure

Now, let’s learn how to code for unit testing. An individual testcase is created by subclassing unittest.TestCase. By overriding or adding appropriate functions, we can add logic to test. The following code will be succeeded if a is equals to b.

import unittest

class Testing(unittest.TestCase):
    def test_string(self):
        a = 'some'
        b = 'some'
        self.assertEqual(a, b)

    def test_boolean(self):
        a = True
        b = True
        self.assertEqual(a, b)

if __name__ == '__main__':

How to run python unittest module

If you’re using PyCharm IDE, you can simply press ctrl+shift+F10 to run unittest module. Otherwise you can use command prompt to run this module. For example, we named the file for unit-testing as Basic_Test.py. So the command to run python unittest will be: $python3.6 -m unittest Basic_Test.Testing If you want to see the verbose, then the command will be; $python3.6 -m unittest -v Basic_Test.Testing By using the PyCharm, we get the below output. Python unittest, python unit test example

Python Unit Test Outcome & Basic Functions

This unittest has 3 possible outcomes. They are mentioned below:

  1. OK: If all test cases are passed, the output shows OK.
  2. Failure: If any of test cases failed and raised an AssertionError exception
  3. Error: If any exception other than AssertionError exception is raised.

There are several function under unittest module. They are listed below.

Method Checks that
assertEqual(a,b) a==b
assertNotEqual(a,b) a != b
assertTrue(x) bool(x) is True
assertFalse(x) bool(x) is False
assertIs(a,b) a is b
assertIs(a,b) a is b
assertIsNot(a, b) a is not b
assertIsNone(x) x is None
assertIsNotNone(x) x is not None
assertIn(a, b) a in b
assertNotIn(a, b) a not in b
assertIsInstance(a, b) isinstance(a, b)
assertNotIsInstance(a, b) not isinstance(a, b)

Python unit test example

Now it’s time to write unit tests for our source class Person. In this class we have implemented two function - get_name() and set_name(). Now, we will test those function using unittest. So we have designed two test cases for those two function. Have a look at the following code, you will understand it easily.

import unittest

# This is the class we want to test. So, we need to import it
import Person as PersonClass

class Test(unittest.TestCase):
    The basic class that inherits unittest.TestCase
    person = PersonClass.Person()  # instantiate the Person Class
    user_id = []  # variable that stores obtained user_id
    user_name = []  # variable that stores person name

    # test case function to check the Person.set_name function
    def test_0_set_name(self):
        print("Start set_name test\n")
        Any method which starts with ``test_`` will considered as a test case.
        for i in range(4):
            # initialize a name
            name = 'name' + str(i)
            # store the name into the list variable
            # get the user id obtained from the function
            user_id = self.person.set_name(name)
            # check if the obtained user id is null or not
            self.assertIsNotNone(user_id)  # null user id will fail the test
            # store the user id to the list
        print("user_id length = ", len(self.user_id))
        print("user_name length = ", len(self.user_name))
        print("\nFinish set_name test\n")

    # test case function to check the Person.get_name function
    def test_1_get_name(self):
        print("\nStart get_name test\n")
        Any method that starts with ``test_`` will be considered as a test case.
        length = len(self.user_id)  # total number of stored user information
        print("user_id length = ", length)
        print("user_name length = ", len(self.user_name))
        for i in range(6):
            # if i not exceed total length then verify the returned name
            if i < length:
                # if the two name not matches it will fail the test case
                self.assertEqual(self.user_name[i], self.person.get_name(self.user_id[i]))
                print("Testing for get_name no user test")
                # if length exceeds then check the 'no such user' type message
                self.assertEqual('There is no such user', self.person.get_name(i))
        print("\nFinish get_name test\n")

if __name__ == '__main__':
    # begin the unittest.main()

Note that the unittest module executes the test functions in the order of their name, not in the order they are defined. And since we want our set_name test to execute first, we have named our test case functions as test_0_set_name and test_1_get_name.

Python Unit Test Example Output

Below images show the output produced by our unit test program - both in normal mode and in verbose mode. Python unit test example python unittest tutorial

$ python3.6 -m unittest -v PersonTest.Test
test_0_set_name (PersonTest.Test) ... Start set_name test

user_id length =  4
[0, 1, 2, 3]
user_name length =  4
['name0', 'name1', 'name2', 'name3']

Finish set_name test

test_1_get_name (PersonTest.Test) ... 
Start get_name test

user_id length =  4
user_name length =  4
Testing for get_name no user test
Testing for get_name no user test

Finish get_name test


Ran 2 tests in 0.000s


That’s all about Python unittest tutorial. To learn more, read the Official Documentation. For any further query please use the comment box. :)

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DigitalOcean Employee
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June 22, 2020

Best article I have found on python unittest!

- Max

    DigitalOcean Employee
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    June 16, 2020

    How can I like this article? it is so cool! thank you very much Pankaj!

    - avi

      DigitalOcean Employee
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      June 5, 2018

      Hi! After running: $python3.6 -m unittest Basic_Test.Testing I get the following error: "ERROR: Basic_Test (unittest.loader._FailedTest) ---------------------------------------------------------------------- ImportError: Failed to import test module: Basic_Test Traceback (most recent call last): File “C:\Users (…) loader.py”, line 154, in loadTestsFromName module = __import__(module_name) ModuleNotFoundError: No module named ‘Basic_Test’ What did I do wrong?

      - Simon

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