Testing has always been a part of software development. However, the world was introduced to a new concept called automated testing when Kent Beck and Erich Gamma introduced JUnit for Java development (http://junit.org). It was based on Kent's earlier work with Smalltalk and automated testing (http://www.xprogramming.com/testfram.htm). In this day and age, automated testing has become a well-accepted concept in the software industry.

A Python version, originally dubbed PyUnit, was created in 1999 and added to Python's standard set of libraries later in 2001 in Python 2.1 (http://docs.python.org/library/unittest.html). Since then, the Python community referred to it as unittest, the name of the library imported into the test code.

Unittest is the foundation of automated testing in the Python world. In this chapter, we will explore the basics of testing and asserting code functionality, building suites of tests, test situations to avoid, and finally testing edges, and corner cases.

For all the recipes in this chapter, we will use virtualenv (http://pypi.python.org/pypi/virtualenv) to create a controlled Python runtime environment. Unittest is part of the standard library, which requires no extra installation steps. But, in later chapters, using virtualenv will allow us to conveniently install other test tools without cluttering up our default Python installation.