The correct way to develop any piece of code is to use automatic testing. The advantages are:

• The automated repetition of a large number of tests after every code refactoring and before any new versions are launched.
• Silent documentation of the use of the code.
• Documentation of the test coverage of your code: Did things work before a change or was a certain aspect never tested?

Changes in the program and in particular in its structure that do not affect its functionality are called code refactoring.

We suggest developing tests in parallel to coding. Good design of tests is an art of its own and there is rarely an investment that guarantees such a good pay-off in development time savings as the investment in good tests.

Now we will go through the implementation of a simple algorithm with the automated testing methods in mind.