JUnit Frequently Asked Questions

  • Can't find the test classes when running them with a TestRunner
  • How do I implement a test case for a thrown exception?
  • How do I organize my test cases?
  • I get a ClassNotFoundException when I use the Swing or AWT TestRunners
  • Different behavior in textui runner?
  • I get ClassCastException when I ran my EJB tests.
  • Where are the test runner properties documented?
  • How do I run setup code once for all my TestCases?
  • I want to debug when a test fails


    • Can't find my test class when using a TestRunner

    When you are getting a "Can't find 'TestClass'" error message when you try to run your test with a TestRunner make sure that: Notice, that the tests that come with the JUnit distribution are not included inside the junit.jar but they reside in the installation directory. Therefore make sure that the JUnit installation directory is on the class path.

    How do I implement a test case for a thrown exception?

    Catch the exception and if it isn't thrown call the fail method. Fail signals the failure of a test case. Here is an example:
    public void testIndexOutOfBoundsException() {
        Vector v= new Vector(10)
        try {
             Object o= v.elementAt(v.size());
             fail("Should raise an ArrayIndexOutOfBoundsException");
        } catch (ArrayIndexOutOfBoundsException e) {
        }
    }
    or use the ExceptionTestCase as follows.
    1) make your TestCase class a subclass of ExceptionTestCase.
    2) write the test ignoring exceptions
    public void testIndexOutOfBoundsException() {
        Vector v= new Vector(10);
        v.elementAt(v.size());
    }
    3) create the TestCase:
        Test t= new ExceptionTestCase("testIndexOutOfBoundsException", ArrayIndexOutOfBoundsException.class)

    Looking at this again, the first way is simpler. Sigh...

    How do I organize my Test Cases?

    Here is one way:
    1. create a test package for each of your application packages. For example, for a package myapp.util define myapp.utiltest. Put all the fixtures for the util package into this package.
    2. in myapp.utiltest define a class which creates a suite with all the tests in this package. To do so define a class AllTests which includes a single static suite method. Here is an example:

      3.  public static Test suite() {
        TestSuite suite= new TestSuite();
        suite.addTest(Fixture1.suite());
        suite.addTest(Fixture2.suite());
        return suite;
       }
    3. define similar AllTests classes that create higher level suites containing the suites from other test packages.
    When the fixtures are in a separate test package  the test cases don't have access to the methods and fields with default visibility ("package visible"). A variation of the above convention is to put all fixtures into the application package itself. This gives the fixtures access to all the package visible methods and fields. To separate the fixture classes from the production classes put them into a separate directory that you then add to the CLASSPATH. This makes it easy to ship the production classes independent of the fixtures. Here is an example for how to do this:
    1. put the fixtures classes for myapp.util into a TESTDIR\tests\myapp\util directory,
    2. add the tests directory to your CLASSPATH.

    How do I run setup code once for all my TestCases?

    Wrap the top level suite in a subclass of TestSetup. Here is a sample AllTests.suite() method:
    public static Test suite() {
      TestSuite suite= new TestSuite();
      ...add your tests and suites here...
      TestSetup wrapper= new TestSetup(suite) {
       public void setUp() {
        oneTimeSetUp();
       }
      };
      return wrapper;
    }

    I get a ClassNotFoundException when I use the LoadingTestRunner

    The UI test runners use a custom class loader to reload your code by default. You can specify a list of excluded package prefixes that shouldn't be reloaded for each test run. The idea is that you typically have a working set of classes that you work with and that there is a set of classes that you don't change. The list of package prefixes is defined in the properties file junit/runner/excluded.properties. As we deliver it, this file excludes the packages that come with jdk1.2 from reloading:
    #
    # The list of excluded package paths for the TestCaseClassLoader
    #
    excluded.0=sun.*
    excluded.1=com.sun.*
    excluded.2=org.omg.*
    excluded.3=javax.*
    excluded.4=sunw.*
    If you are using additional jars from 3rd party vendors you can either:

    I want to debug when a test fails

    Start the test runner under the debugger and configure the debugger so that it catches the junit.framework.AssertionFailedError. How you do this depends on the used IDE. Most Java debuggers support to stop the program when a specific exception is fired. Notice, that this will only break into the debugger when an "anticipated" assertion failed error occurs.

    My tests pass in the textui runner but they fail in the UI testrunners?

    The UI test runner use a custom class loader by default to reload classes for each run. The textui runner is using the system class loader. To disable the custom class loader uncheck the "Reload classes for each run" check box. The default setting can be changed in the junit.properties file.

    Where are the test runner properties documented?

    See the JUnit Properties documentation.
     

    I get a ClassCastException in the Swing or AWT TestRunners

    When I use the textui.TestRunner my setup runs OK. I get a ClassCastException when I call PortableRemoteObject.narrow(SomeJndiObject,Some.class).
    This is a consequence of the class reloading feature of the UI test runners. There are different way to avoid this problem: