| The code examples shown so far use plain asserts . These are the most generic type of test assertion, which take a Boolean condition that must evaluate to TRUE for the test to succeed. A plain assert, the unit test for the Library method removeBook( ) , is shown in Example 4-1. Example 4-1. Test method testRemoveBook( ) using a plain assert LibraryTest.java public void testRemoveBook ( ) { library.removeBook( "Dune" ); Book book = library.getBook( "Dune" ); assertTrue( book == null ); }
If the method removeBook( ) is stubbed out, the test fails. The following test results report the failure: > java junit.textui.TestRunner LibraryTests .....F. Time: 0.06 There was 1 failure: 1) testRemoveBook(LibraryTest)junit.framework.AssertionFailedError at LibraryTest.testRemoveBook(LibraryTest.java:32) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) FAILURES!!! Tests run: 6, Failures: 1, Errors: 0
Although the line of code where the failure occurred is shown, the output does not describe the specific cause of the failure. It often is helpful to add an informative message to the assertion. The xUnits generally have two versions of every assert method, one of which takes a message parameter describing the assert. Example 4-2 shows the test method using an assert with a message. Example 4-2. Test method using an assert with a message LibraryTest.java public void testRemoveBook ( ) { library.removeBook( "Dune" ); Book book = library.getBook( "Dune" ); assertTrue( " book is not removed" , book == null ); }
With the additional message, the rest results provide better information about the cause of the test failure: 1) testRemoveBook(LibraryTest)junit.framework.AssertionFailedError: book is not removed
Although all assert conditions ultimately must evaluate to a Boolean result of TRUE or FALSE , it can be tedious to constantly reduce every expression to this form. The xUnits offer a variety of assert functions to help. Examples of several of the assert methods from JUnit are as follows : assertFalse( book == null ); assertFalse( "book is null", book == null ); assertNull( book ); assertNull( "book is not null", book ); assertNotNull( book ); assertNotNull( "book is null", book ); assertEquals( "Solaris", book.title ); assertEquals( "unexpected book title", "Solaris", book.title );
These assert methods all have variants that take a message parameter to describe the failure, as shown above. The assertEquals() method has variants that take different data types as arguments. | 