In software development, unit testing is a software testing method in which the smallest testable parts of source code, called units, are individually and independently tested to determine whether they behave exactly as we expect. To unit test our source code, all we need is a test program that can run a bit of our source code (unit), provide some inputs to each unit, and check the results for the expected output. Most unit tests are written using some sort of test framework set of library code designed to make writing and running tests easier. One such framework is called JUnit. It is a unit testing framework for the Java programming language.
Let's see how to test one of our domain objects using the JUnit framework to ensure it functions as expected. In an earlier chapter, we created a domain object to represent an item in a shopping cart called CartItem. The CartItem class has a method called getTotalPrice to return the total price...