Expert Python Programming - Third Edition

Three simple steps of test-driven development

The test-driven development process, in its simplest form, consists of the following three steps:

1. Writing automated tests for a new functionality or improvement that was not implemented yet.
2. Providing minimal code that just passes all the defined tests.
3. Refactoring code to meet the desired quality standards.

The most important fact to remember about this development cycle is that tests should be written before actual implementation. It is not an easy task for inexperienced developers, but it is the only approach that reliably guarantees that the code you are going to write will be testable.

For example, a developer who is asked to write a function that checks whether the given number is a prime ...