To be able to write a unit test, we need to write a method that follows the method signature requirements (input and output), but we will just let it return null. By doing this, we can write a unit test, see it fail, and then provide the correct implementation and see the test succeed.
If you study the business rules closely, you'll find that you have to write a method that would take an input and generate a response. The method has to be self-contained; it does not seem to require any class instance variables or methods. We, therefore, will choose to write a static class method. During the coding of the unit test, we can determine whether this was a bad choice. If so, we can always change it ...
