Writing Robust Code and Unit Testing

Introduction

Our previous lessons have introduced the basic tools of programming: variables and lists, file I/O, loops, conditionals, and most importantly, functions. What they haven’t done is show us how to tell if a program is getting the right answer. For the sake of argument, if each line we write has a 99% chance of being right, then a 70-line program will be wrong more than half the time. We need to do better than that, which means we need to:

• write programs that check their own operation; and
• write tests to catch the mistakes those self-checks miss.

Learning Objectives

• how to write code defensively to guard against making errors;
• how to use a unit testing framework;
• when it’s useful to write tests before writing code.
• how Python reports and handles errors;