Chapter 40: Testing

Complete Python lesson for very beginners. Technical words are explained in simple language, and every outline topic includes a practical example, expected output, steps, and practice.

Python CourseVery Beginner Friendly15 TopicsExamples + Output20 Q&A

Chapter 40 · 15 topics

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Chapter Overview

This Python tutorial chapter covers Testing through 15 connected topics. Work through the examples in order, check the expected output, and complete the practice after each topic.

40.1 Why Test Software?
40.2 Unit Tests
40.3 unittest
40.4 Test Cases
40.5 Assertions
Plus 10 additional Python topics in this chapter.

40.1 Why Test Software?

Why Test Software? is part of Testing. In simple language, it means a Python idea used while learning testing.

It makes programs easier to trust, diagnose, change, and maintain as they become larger. For a very beginner, focus first on what goes in, what Python does, and what comes out; details become easier after you run a small example.

Technical words in simple language: Why Test Software? (a Python idea used while learning testing).

Python / Practical Example

import unittest

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

class AddTest(unittest.TestCase):
    def test_add(self):
        self.assertEqual(add(2, 3), 5)

result = unittest.TextTestRunner(verbosity=0).run(unittest.defaultTestLoader.loadTestsFromTestCase(AddTest))
print(result.wasSuccessful())

Expected Output

True

Step-by-Step Explanation

Define behavior to test.
Create a TestCase method whose name begins with test.
Run the test and check that it succeeds.

Practice: Re-type the example for “Why Test Software?”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

40.2 Unit Tests

Unit Tests is part of Testing. In simple language, it means a Python idea used while learning testing.

Technical words in simple language: Unit Tests (a Python idea used while learning testing).

Python / Practical Example

import unittest

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

class AddTest(unittest.TestCase):
    def test_add(self):
        self.assertEqual(add(2, 3), 5)

result = unittest.TextTestRunner(verbosity=0).run(unittest.defaultTestLoader.loadTestsFromTestCase(AddTest))
print(result.wasSuccessful())

Expected Output

True

Step-by-Step Explanation

Define behavior to test.
Create a TestCase method whose name begins with test.
Run the test and check that it succeeds.

Practice: Re-type the example for “Unit Tests”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

40.3 unittest

unittest is part of Testing. In simple language, it means a Python idea used while learning testing.

Technical words in simple language: unittest (a Python idea used while learning testing).

Python / Practical Example

import unittest

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

class AddTest(unittest.TestCase):
    def test_add(self):
        self.assertEqual(add(2, 3), 5)

result = unittest.TextTestRunner(verbosity=0).run(unittest.defaultTestLoader.loadTestsFromTestCase(AddTest))
print(result.wasSuccessful())

Expected Output

True

Step-by-Step Explanation

Define behavior to test.
Create a TestCase method whose name begins with test.
Run the test and check that it succeeds.

Practice: Re-type the example for “unittest”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

40.4 Test Cases

Test Cases is part of Testing. In simple language, it means a Python idea used while learning testing.

Technical words in simple language: Test Cases (a Python idea used while learning testing).

Python / Practical Example

import unittest

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

class AddTest(unittest.TestCase):
    def test_add(self):
        self.assertEqual(add(2, 3), 5)

result = unittest.TextTestRunner(verbosity=0).run(unittest.defaultTestLoader.loadTestsFromTestCase(AddTest))
print(result.wasSuccessful())

Expected Output

True

Step-by-Step Explanation

Define behavior to test.
Create a TestCase method whose name begins with test.
Run the test and check that it succeeds.

Practice: Re-type the example for “Test Cases”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

40.5 Assertions

Assertions is part of Testing. In simple language, it means a Python idea used while learning testing.

It is one building block of testing and helps you write clearer, more predictable Python programs. For a very beginner, focus first on what goes in, what Python does, and what comes out; details become easier after you run a small example.

Technical words in simple language: Assertions (a Python idea used while learning testing).

Python / Practical Example

total = 5
assert total >= 0
print("valid")

Expected Output

valid

Step-by-Step Explanation

assert checks a condition during development.
No exception occurs because the condition is true.
Do not use assertions as a substitute for user-input validation.

Practice: Re-type the example for “Assertions”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

40.6 Setup and Teardown

Setup and Teardown is part of Testing. In simple language, it means a collection of unique values.

It helps you prepare a reliable Python workspace so the same commands and files run in the environment you expect. For a very beginner, focus first on what goes in, what Python does, and what comes out; details become easier after you run a small example.

Technical words in simple language: Setup and Teardown (a collection of unique values).

Python / Practical Example

assert 2 + 2 == 4
print("test passed")

Expected Output

test passed

Step-by-Step Explanation

Read the example from top to bottom.
Identify the value, object, or operation related to this topic.
Change one small input and predict the result before running it.

Practice: Re-type the example for “Setup and Teardown”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

40.7 Test Discovery

Test Discovery is part of Testing. In simple language, it means a Python idea used while learning testing.

Technical words in simple language: Test Discovery (a Python idea used while learning testing).

Python / Practical Example

import unittest

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

class AddTest(unittest.TestCase):
    def test_add(self):
        self.assertEqual(add(2, 3), 5)

result = unittest.TextTestRunner(verbosity=0).run(unittest.defaultTestLoader.loadTestsFromTestCase(AddTest))
print(result.wasSuccessful())

Expected Output

True

Step-by-Step Explanation

Define behavior to test.
Create a TestCase method whose name begins with test.
Run the test and check that it succeeds.

Practice: Re-type the example for “Test Discovery”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

40.8 Test Organization

Test Organization is part of Testing. In simple language, it means a Python idea used while learning testing.

Technical words in simple language: Test Organization (a Python idea used while learning testing).

Python / Practical Example

import unittest

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

class AddTest(unittest.TestCase):
    def test_add(self):
        self.assertEqual(add(2, 3), 5)

result = unittest.TextTestRunner(verbosity=0).run(unittest.defaultTestLoader.loadTestsFromTestCase(AddTest))
print(result.wasSuccessful())

Expected Output

True

Step-by-Step Explanation

Define behavior to test.
Create a TestCase method whose name begins with test.
Run the test and check that it succeeds.

Practice: Re-type the example for “Test Organization”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

40.9 Mocking Concepts

Mocking Concepts is part of Testing. In simple language, it means a Python idea used while learning testing.

Technical words in simple language: Mocking Concepts (a Python idea used while learning testing).

Python / Practical Example

assert 2 + 2 == 4
print("test passed")

Expected Output

test passed

Step-by-Step Explanation

Read the example from top to bottom.
Identify the value, object, or operation related to this topic.
Change one small input and predict the result before running it.

Practice: Re-type the example for “Mocking Concepts”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

40.10 Integration Tests

Integration Tests is part of Testing. In simple language, it means a Python idea used while learning testing.

Technical words in simple language: Integration Tests (a Python idea used while learning testing).

Python / Practical Example

import unittest

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

class AddTest(unittest.TestCase):
    def test_add(self):
        self.assertEqual(add(2, 3), 5)

result = unittest.TextTestRunner(verbosity=0).run(unittest.defaultTestLoader.loadTestsFromTestCase(AddTest))
print(result.wasSuccessful())

Expected Output

True

Step-by-Step Explanation

Define behavior to test.
Create a TestCase method whose name begins with test.
Run the test and check that it succeeds.

Practice: Re-type the example for “Integration Tests”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

40.11 Functional Tests

Functional Tests is part of Testing. In simple language, it means a reusable block of instructions.

Technical words in simple language: Functional Tests (a reusable block of instructions).

Python / Practical Example

import unittest

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

class AddTest(unittest.TestCase):
    def test_add(self):
        self.assertEqual(add(2, 3), 5)

result = unittest.TextTestRunner(verbosity=0).run(unittest.defaultTestLoader.loadTestsFromTestCase(AddTest))
print(result.wasSuccessful())

Expected Output

True

Step-by-Step Explanation

Define behavior to test.
Create a TestCase method whose name begins with test.
Run the test and check that it succeeds.

Practice: Re-type the example for “Functional Tests”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

40.12 Regression Tests

Regression Tests is part of Testing. In simple language, it means a Python idea used while learning testing.

Technical words in simple language: Regression Tests (a Python idea used while learning testing).

Python / Practical Example

import unittest

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

class AddTest(unittest.TestCase):
    def test_add(self):
        self.assertEqual(add(2, 3), 5)

result = unittest.TextTestRunner(verbosity=0).run(unittest.defaultTestLoader.loadTestsFromTestCase(AddTest))
print(result.wasSuccessful())

Expected Output

True

Step-by-Step Explanation

Define behavior to test.
Create a TestCase method whose name begins with test.
Run the test and check that it succeeds.

Practice: Re-type the example for “Regression Tests”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

40.13 Test Coverage

Test Coverage is part of Testing. In simple language, it means a Python idea used while learning testing.

Technical words in simple language: Test Coverage (a Python idea used while learning testing).

Python / Practical Example

import unittest

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

class AddTest(unittest.TestCase):
    def test_add(self):
        self.assertEqual(add(2, 3), 5)

result = unittest.TextTestRunner(verbosity=0).run(unittest.defaultTestLoader.loadTestsFromTestCase(AddTest))
print(result.wasSuccessful())

Expected Output

True

Step-by-Step Explanation

Define behavior to test.
Create a TestCase method whose name begins with test.
Run the test and check that it succeeds.

Practice: Re-type the example for “Test Coverage”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

40.14 Test-Driven Development

Test-Driven Development is part of Testing. In simple language, it means a Python idea used while learning testing.

Technical words in simple language: Test-Driven Development (a Python idea used while learning testing).

Python / Practical Example

import unittest

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

class AddTest(unittest.TestCase):
    def test_add(self):
        self.assertEqual(add(2, 3), 5)

result = unittest.TextTestRunner(verbosity=0).run(unittest.defaultTestLoader.loadTestsFromTestCase(AddTest))
print(result.wasSuccessful())

Expected Output

True

Step-by-Step Explanation

Define behavior to test.
Create a TestCase method whose name begins with test.
Run the test and check that it succeeds.

Practice: Re-type the example for “Test-Driven Development”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

40.15 Testing Best Practices

Testing Best Practices is part of Testing. In simple language, it means checking software behavior against expected results.

Technical words in simple language: Testing Best Practices (checking software behavior against expected results).

Python / Practical Example

import unittest

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

class AddTest(unittest.TestCase):
    def test_add(self):
        self.assertEqual(add(2, 3), 5)

result = unittest.TextTestRunner(verbosity=0).run(unittest.defaultTestLoader.loadTestsFromTestCase(AddTest))
print(result.wasSuccessful())

Expected Output

True

Step-by-Step Explanation

Define behavior to test.
Create a TestCase method whose name begins with test.
Run the test and check that it succeeds.

Practice: Re-type the example for “Testing Best Practices”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

Common Beginner Mistakes

Copying code without predicting what each line does.
Ignoring the first useful error message or traceback location.
Mixing tabs/spaces or changing indentation accidentally.
Using data of the wrong type for an operation.
Trying to learn many advanced variations before mastering one small working example.

Chapter Practice

Choose three topics from this chapter and re-type their examples without copying and pasting.
For each example, change one input and predict the output first.
Explain five technical terms from this chapter in your own beginner-friendly words.
Create one small program that combines at least two chapter topics.
Keep notes about errors you made and what fixed them.

Mini Project / Challenge

Create a small Python exercise that combines at least three ideas from Testing. Start with a tiny working version, test it, then improve it one step at a time.

Choose three topics from this chapter.
Write or adapt a small Python example using those topics.
Predict the output before running the code.
Test at least one different input.
Write two sentences explaining what the program does and what you learned.

20 Questions & Answers

1. What is the main goal of Chapter 40?

The goal is to understand testing through small explanations, examples, and practice.

2. Should I memorize every command or method?

No. Understand the pattern, practice the common form, and learn how to read documentation when you need exact details.

3. Why are the examples small?

Small examples isolate one idea at a time, which makes errors easier to understand and fix.

4. What should I do when an example gives an error?

Read the last part of the traceback, check spelling and indentation, confirm the required package or file exists, and compare the input types with what the operation expects.

5. Why should I predict output before running code?

Prediction forces you to reason about the program instead of only copying it.

6. What should I remember about Why Test Software??