Like visits to the dentist, thorough testing of any program is something that you should be doing if you want to avoid the pain of having to trace a problem that you thought you'd taken care of. This lesson is one that normally takes a programmer many years to learn, and to be honest, you're still going to be working on it for many years. However, the one thing that is of the utmost importance is that testing must be organized; and to be the most effective, you must start writing your programs knowing that it will be tested as you go along, and plan around having the time to write and confirm your test cases.

Fortunately, Python offers an excellent facility for organizing your testing called PyUnit. It is a Python port of the Java JUnit package, so if you've worked with JUnit, you're already on firm ground when testing in Python—but if not, don't worry. This chapter will show you the following:

□ The concept and use of assertions

□ The basic concepts of unit testing and test suites

□ A few simple example tests to show you how to organize a test suite

□ Thorough testing of the search utility from Chapter 11

The beauty of PyUnit is that you can set up testing early in the software development life cycle, and you can run it as often as needed while you're working. By doing this, you can catch errors early on, before they're painful to rework — let alone before anybody else sees them. You can also set up test cases before you write code, so that as you write, you can be sure that your results match what you expect! Define your test cases before you even start coding, and you'll never find yourself fixing a bug only to discover that your changes have spiraled out of control and cost you days of work.

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