Python - Working Code Sample

Working Code Sample for Testing in Python

Introduction

Testing is a fundamental part of software development. In Python, it’s essential to write testable code and accompany it with test cases to ensure reliability and robustness. This document provides a working code sample for a realistic Python project and demonstrates how to write corresponding test cases using Python's built-in unittest framework.

Project Overview

We will build a small project consisting of a library management system. The project will include classes for Book and Library, along with methods to add, remove, and search for books. Each functionality will be accompanied by test cases that follow best practices.

Library System Code

book.py

class Book:
    def __init__(self, title, author, year):
        self.title = title
        self.author = author
        self.year = year

    def __str__(self):
        return f"{self.title} by {self.author} ({self.year})"

    def __eq__(self, other):
        return (
            self.title == other.title and
            self.author == other.author and
            self.year == other.year
        )

library.py

from book import Book

class Library:
    def __init__(self):
        self.books = []

    def add_book(self, book):
        if book in self.books:
            return False
        self.books.append(book)
        return True

    def remove_book(self, book):
        if book in self.books:
            self.books.remove(book)
            return True
        return False

    def find_books_by_author(self, author):
        return [book for book in self.books if book.author == author]

    def find_books_by_title(self, title):
        return [book for book in self.books if book.title == title]

    def list_books(self):
        return sorted(self.books, key=lambda x: (x.author, x.title))

Writing Tests Using unittest

test_library.py

import unittest
from library import Library
from book import Book

class TestLibrary(unittest.TestCase):
    def setUp(self):
        self.library = Library()
        self.book1 = Book("1984", "George Orwell", 1949)
        self.book2 = Book("Animal Farm", "George Orwell", 1945)
        self.book3 = Book("Brave New World", "Aldous Huxley", 1932)

    def test_add_book(self):
        result = self.library.add_book(self.book1)
        self.assertTrue(result)
        self.assertIn(self.book1, self.library.books)

    def test_add_duplicate_book(self):
        self.library.add_book(self.book1)
        result = self.library.add_book(self.book1)
        self.assertFalse(result)

    def test_remove_book(self):
        self.library.add_book(self.book1)
        result = self.library.remove_book(self.book1)
        self.assertTrue(result)
        self.assertNotIn(self.book1, self.library.books)

    def test_remove_nonexistent_book(self):
        result = self.library.remove_book(self.book1)
        self.assertFalse(result)

    def test_find_books_by_author(self):
        self.library.add_book(self.book1)
        self.library.add_book(self.book2)
        self.library.add_book(self.book3)
        results = self.library.find_books_by_author("George Orwell")
        self.assertIn(self.book1, results)
        self.assertIn(self.book2, results)
        self.assertNotIn(self.book3, results)

    def test_find_books_by_title(self):
        self.library.add_book(self.book1)
        results = self.library.find_books_by_title("1984")
        self.assertEqual(results, [self.book1])

    def test_list_books(self):
        self.library.add_book(self.book1)
        self.library.add_book(self.book2)
        self.library.add_book(self.book3)
        books = self.library.list_books()
        expected_order = sorted([self.book1, self.book2, self.book3], key=lambda x: (x.author, x.title))
        self.assertEqual(books, expected_order)

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

Test Output

When running test_library.py with python -m unittest test_library.py, you should see output like:

.......
----------------------------------------------------------------------
Ran 7 tests in 0.001s

OK

This working code sample demonstrates a complete, real-world example of how to structure Python code and write effective tests. It shows how to:

• Create a basic model with classes
• Use unittest to test class behaviors
• Organize code and tests in separate files

With these techniques, developers can confidently write, test, and refactor code while ensuring correctness and stability in their Python projects.