Chapter 11. Testing Your Code

Learn how to test code using Python's unittest module.

Testing a Function

Function to be tested as shown below.

def get_formatted_name(first, last):
    """Generate a neatly formatted full name."""
    full_name = f"{first} {last}"
    return full_name.title()

A script that should use get_formatted_name

from name_function import get_formatted_name

print("Enter 'q' at any time to quit.")
while True:
    first = input("\nPlease give me a first name: ")
    if first == 'q':
        break
    last = input("Please give me a last name: ")
    if last == 'q':
        break

    formatted_name = get_formatted_name(first, last)
    print(f"\tNeatly formatted name: {formatted_name}.")

To make sure get_formatted_name function properly, using unittest module of Python

import unittest
from name_function import get_formatted_name

class NamesTestCase(unittest.TestCase):
    """Test for name_function.py"""

    def test_first_last_name(self):
        """Do names like 'Janis Joplin' work?"""
        formatted_name = get_formatted_name('janis', 'joplin')
        self.assertEqual(formatted_name, 'Janis Joplin')

if __name__ == '__main__':
    unittest.main()

Key points:

Import unittest module as shown
Import function to be tested
Here, unittest's most useful feature assert is used. assertEqual can compare two objects
__name__ is a special variable, which is set when the program is executed. If the file is being run as the main program, the value of __name__ is set to '__main__'

Result of running this test:

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

OK

First dot represent the single test passed.

A Failing Test

Failure case returns

F
======================================================================
FAIL: test_first_last_name (__main__.NamesTestCase)
Do names like 'Janis Joplin' work?
----------------------------------------------------------------------
Traceback (most recent call last):
  File "test_name_function.py", line 10, in test_first_last_name
    self.assertEqual(formatted_name, 'Janis Joplins')
AssertionError: 'Janis Joplin' != 'Janis Joplins'
- Janis Joplin
+ Janis Joplins
?             +


----------------------------------------------------------------------
Ran 1 test in 0.001s

FAILED (failures=1)

Highlight:

FAIL: test_first_last_name tell's where the error coming from.

Fix them

If employing TDD, we can first create test case, then develop code to be test against.

Testing a Class

e.g. above shown how to write test case for single function, we also need to write test for class.

A Variety of Assert Methods

Python unittest module provide various assert methods in unittest.TestCase class.

List of available assert methods

Method	Use
`assertEqual(a,b)`	Verify `a == b`
`assertNotEqual(a,b)`	Verify that `a != b`
`assertTrue(x)`	Verify that x is True
`assertFalse(x)`	Verify that x is False
`assertIn(item, list)`	Verify that item is in list
`assertNotIn(item, list)`	Verrify that item is not in list

A Class to Test

Steps to write test case:

Importing unittest module and class to test
Creating a test class to inherit from unittest.TestCase
Creating test function under class
1. Create an instance of the class to be tested.
2. Verify its operation

e.g.

class to be tested in survey.py have class AnonymousSurvey
script to use class language_survey
test script as shown below:

import unittest
from survey import AnonymousSurvey

class TestAnonymousSurvey(unittest.TestCase):
    """Tests for the class AnonymouseSurvey"""
    
    def test_store_single_response(self):
        """Tests that a single response is stored properly"""
        question = "What language did you first learn to speak?"
        my_survey = AnonymousSurvey(question)
        my_survey.store_response('English')
        self.assertIn('English', my_survey.responses)

    def test_store_three_responses(self):
        """Test that three individual responses are stored properly"""
        question = "What language did you first learn to speak?"
        my_survey = AnonymousSurvey(question)
        responses = ['English', 'Spanish', 'Mandarin']
        
        # Store responses
        for response in responses:
            my_survey.store_response(response)
        
        # Test my_survey operation
        for response in responses:
            self.assertIn(response, my_survey.responses)

if __name__ == '__main__':
    unittest.main()

We can add more test functions to test different scenario. But it's too repetitive. Use setUp()

The setUp() Method

We can use setUp() to setup initial states of self.my_survey, which can reduce repetitions.

import unittest
from survey import AnonymousSurvey

class TestAnonymousSurvey(unittest.TestCase):
    """Tests for the class AnonymouseSurvey"""
    
    def setUp(self):
        """
        Create a survey and a set of responses for use in all test methods.
        """
        question = "What language did you first learn to speak?"
        self.my_survey = AnonymousSurvey(question)
        self.responses = ['English', 'Spanish', 'Mandarin']

    def test_store_single_response(self):
        """Test test a single response is stored properly"""
        self.my_survey.store_response(self.responses[0])
        self.assertIn(self.responses[0], self.my_survey.responses)

    def test_store_three_responses(self):
        """Test that three individual responses are stored properly."""
        for response in self.responses:
            self.my_survey.store_response(response)
        for response in self.responses:
            self.assertIn(response, self.my_survey.responses)

if __name__ == '__main__':
    unittest.main()

Use setUp() can make test methods easier to write.
We can make one set of instances and attributes in setUp() and then use these instances in all your test methods.

Note of unittest

When a test case is running, Python prints one character for each unit test as it's completed.
A passing test prints a dot .
A test that results in an error prints an E
A test that results in failed assertion prints an F.
Hence, we can see a different number of dots and characters on the first line of output when you run your test cases.

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