Java™ Application Development on Linux - Dator

13.4 Installing and Running JUnit297Let’s apply that approach to our previous design discussion. We’ve describedan Account class in our design discussion. It needs a name, an owner,and an amount of money when created. It should have a method to createsubaccounts, ones that are connected to this account and get allocated some orall of the main account’s money.Example 13.1 is the basic structure of our Account class.That’s enough to begin writing a test. We have described the constructor,with the three parameters that it will need. We’ve also described a method onthe Account object, one that will create subaccounts. That gives us enoughinformation to write a test that will create an account and then create subaccountsof that account. We can test to see if the accounts are created properly(i.e., are not null) and if the subaccounts use up all the money of the parentaccount.When you “test then code,” you begin to use the objects that you havedesigned without getting bogged down in their implementation. You are, ineffect, describing their external interfaces without implementing them. You arealso beginning to use the classes as a user might, though a tester’s use is a bitdifferent than the way an application might use them. However, as a user ofthese classes you are beginning to test the design, by testing the results of theuse cases—are these classes really usable?You may discover that you need some additional functionality. In our example,we can see from the description of our test that we will need a gettermethod on the account to return the amount of money that remains unallocatedto subaccounts. Then we can test to see if it gets used up properly.There are many more test cases that we could develop for the Accountclass, but let’s use just these for now, so that the size of our test case ismanageable.Our next step is to get JUnit installed before we get too deep intodeveloping our test cases. That will give us something to run these tests.13.4INSTALLING AND RUNNING JUNITIt’s rather simple to install a standalone version of JUnit. We download a ZIPfile from the JUnit Web site, then unzip it into a directory. Adding the JUnitJAR file to your CLASSPATH is all that’s needed to make JUnit available for youto run it.