Coding, Testing, and Documentation: the Virtuous Cycle

We write software because we want it to do something useful. But how do we know that the code does what we want it to? The obvious answer is that we test it. Sometimes we run a piece of code we've just written and look at what it does, to see if it is doing the right thing. There's often a lot of code, though, and there are a lot of things we want to ensure are working—and continue to work as we add new features.

Thankfully, most languages come with a way to automate testing your code, and Python is no exception. When we create tests along with the code we are writing, it will increase the likelihood of spotting an error. Bugs in our code cost time, and can cost a company money. Bugs are also impossible to eliminate completely—the best we can do is take reasonable steps to prevent as many as we can.

Writing tests helps to provide a clearer idea of what software is meant to do. Take, for...