Writing and running JUnit tests

In this section, you will be using the JUnit testing framework to write and run tests. To get started with JUnit you can refer to the JUnit Cookbook.

Writing Tests

Create a project "JUnitTest". Now you can write your first test. You implement the test in a subclass of TestCase. You can do so either using the standard Class wizard or the specialized Test Case wizard:

  1. Open the New wizard (File > New > JUnit Test Case).
  2. Select New JUnit 3 test and enter "TestFailure" as the name of your test class:

    TestCase creation wizard page 1

    Note: If you want to use JUnit 4 tests you have to make sure that your compiler compliance is set to 1.5.

  3. You will see a warning message asking you to add the junit library to the build path. Use the Click here link to add the junit library automatically.
  4. Click Finish to create the test class.

Add a test method that fails to the class TestFailure. A quick way to enter a test method is with the test template. To do so, place the cursor inside the class declaration. Type "test" followed by Ctrl+Space to activate code assist and select the "test" template. Change the name of the created method to testFailure and invoke the fail() method.

public void testFailure() throws Exception {

Now you are ready to run your first test.

Running Tests

To run TestFailure hit the run button in the toolbar. It will automatically run as JUnit Test. You can inspect the test results in the JUnit view. This view shows you the test run progress and status:

Failed test

The view is shown in the current perspective whenever you start a test run. A convenient arrangement for the JUnit view is to dock it as a fast view. The JUnit view has two tabs: one shows you a list of failures and the other shows you the full test suite as a tree. You can navigate from a failure to the corresponding source by double clicking the corresponding line in the failure trace.

Dock the JUnit view as a fast view, remove the fail() statement in the method testFailure() so that the test passes and rerun the test again. You can rerun a test either by clicking the Rerun button in the view's tool bar or you can re-run the program that was last launched by activating the Run drop down. This time the test should succeed. Because the test was successful, the JUnit view doesn't pop up, but the success indicator shows on the JUnit view icon and the status line shows the test result. As a reminder to rerun your tests the view icon is decorated by a "*" whenever you change the workspace contents after the run.

Successful test - A successful test run
Successful test but workspace has changed - A successful test run, but the workspace contents have changed since the last test run.

In addition to running a test case as described above you can also:

Customizing a Test Configuration

When you want to pass parameters or customize the settings for a test run you open the Launch Configuration Dialog. Select Open Run Dialog....in the Run drop-down menu in the toolbar:

JUnit Launch Configuration

In this dialog you can specify the test to be run, its arguments, its run-time class path, and the Java run-time environment.

Debugging a Test Failure

In the case of a test failure you can follow these steps to debug it:

  1. Double click the failure entry from the Failures tab in the JUnit view to open the corresponding file in the editor.
  2. Set a breakpoint at the beginning of the test method.
  3. Select the test case and execute  Debug As>JUnit Test from the Debug drop down.

A JUnit launch configuration has a "keep alive" option. If your Java virtual machine supports "hot code replacement" you can fix the code and rerun the test without restarting the full test run. To enable this option select the Keep JUnit running after a test run when debugging checkbox in the JUnit launch configuration.

Creating a Test Suite

The JUnit TestSuite wizard helps you with the creation of a test suite. You can select the set of classes that should belong to a suite.

  1. Open the New wizard
  2. Select Java > JUnit > JUnit Test Suite and click Next.
  3. Enter a name for your test suite class (the convention is to use "AllTests" which appears by default).

    Test Suite wizard

  4. Select the classes that should be included in the suite. We currently have a single test class only, but you can add to the suite later.

You can add or remove test classes from the test suite in two ways:

Note: the wizard puts 2 markers, //$JUnit-BEGIN$ and //$JUnit-END$, into the created Test suite class, which allows the wizard to update existing test suite classes. Editing code between the markers is not recommended.