We'll work on a variation of a well-known kata called Mars Rover, originally published in Dallas Hack Club (http://dallashackclub.com/rover).

Imagine that a naval ship is placed somewhere on Earth's seas. Since this is the 21^st century, we can control that ship remotely.

Since this is a TDD book and the subject of this chapter is unit tests, we'll develop an application using a TDD approach with the focus on unit tests. In the previous chapter, Chapter 3, Red-Green-Refactor – From Failure Through Success until Perfection, you learned the theory and had practical experience with the Red-Green-Refactor procedure. We'll build on top of that and try to learn how to employ unit testing effectively. Specifically, we'll try to concentrate on a unit we're developing and learn how to isolate and ignore dependencies that a unit might use. Not only that, but we'll try to concentrate on one requirement at a time. For this reason, you were presented only with high-level requirements; we should be able to move the remote-controlled ship, located somewhere on the planet, around.

To make things easier, all the supporting classes have been already made and tested. This will allow us to concentrate on the main task at hand and, at the same time, keep this exercise concise.