While compilers can look for structural problems in a program, they cannot
tell whether the results of a program or method are correct.
developers test their programs to ensure that they behave as expected. This can
be as simple as calling a method in the Interactions Pane to view its results,
but this technique requires you to think about the answers you expect every time
you run any tests. A much better solution is to give the tests the answers you
expect, and let the tests themselves do all the work.
Thankfully, a technique known as unit testing makes this quite easy. You
write many small tests that create your objects and assert that they behave the
way you expect in different situations. A unit test framework known as JUnit
(http://www.junit.org) automates the process of running these tests, letting you
quickly see whether your program returns the results you expect.
DrJava makes the process of running unit tests very simple by providing
support for JUnit. Once you have written a JUnit test class (as described in the
next section), you can simply choose the "Test Current Document" command from
the Tools menu to run the tests and view the results. The name of the tests
being run will be shown in the Test Output tab, with each test method turning
green if it completes successfully and red if it fails. Any failures will be
displayed after the list of methods in the same way as the compiler errors. A
progress bar will keep you updated on how many tests have been run.
Also, clicking the "Test" button on the toolbar or choosing "Test All
Documents" from the Tools menu will run JUnit on any open testcases, making
running multiple test files very simple.