Java™ Application Development on Linux - Dator

308Chapter 13JUnit: Automating Unit TestingThe String message is very helpful when you get large numbers of comparisonsand assertions inside your test cases. It can help you identify whichassert in which test failed.TIPWhen writing your assertions, keep in mind the difference betweenassertEquals() and assertSame(). The latter will test if the two argumentsrefer to the very same instance of an object, whereas the former onlychecks to see that their values are equal. So any two references to objects thatare the same will also be equal, but not vice versa. For example:String sample = "value";String others = "more value".substring(5);assertEquals(sample, others); // will passassertSame(sample, others); // will failDigging a little deeper into how all this works, it might be worth pointingout that the JUnit TestCase class, while an abstract class itself, is also an extensionof another class, the Assert class. The Assert class is the class that definesall these public static methods for asserting the various conditions (see the listabove). That is why you don’t need any qualifiers on the various assert calls.They are all part of your test case by virtue of it extending TestCase. It alsomeans that you could override any of them to get special behavior. This mightbe useful for assertEquals(Object, Object), to allow you to compareobjects of your own kinds, but we don’t recommend this. You are better offoverriding the equals() method of your own object than messing with theJUnit methods. And remember that if you override those behaviors, your testswill only be as good as your implementation of the assert mechanisms.13.5.2 Running a Test CaseRecall how we ran the JUnit self-tests after installation. We can now use asimilar command to execute our own test case. With the CLASSPATH still setas above, try compiling and running the test case:$ javac net/multitool/core/AccountTest.java$ java junit.textui.TestRunner net.multitool.core.AccountTest