Java Extreme Programming Cookbook

Avoiding Swing Threading Problems

Problem

You want to test Swing functions that dispatch to the AWT event queue, such as focus traversal.

Solution

Write a utility method to wait until pending AWT event queue messages are processed.

Discussion

Suppose you want to test the focus traversal order of the PersonEditorPanel introduced in the previous recipe. You want to ensure that focus travels from component to component in the correct order as the user hits the tab key. To do this, you write the following test:

public void testTabOrder(  ) {
    JTextField firstNameField = this.tannerPanel.getFirstNameField(  );

    firstNameField.requestFocusInWindow(  );

    // simulate the user hitting tab
    firstNameField.transferFocus(  );

    // ensure that the last name field now has focus
    JTextField lastNameField = this.tannerPanel.getLastNameField(  );
    assertTrue("Expected last name field to have focus",
            lastNameField.hasFocus(  ));
}

As written, this test fails. First and foremost, the components must be visible on screen before they can obtain focus. So you try modifying your setUp( ) method as follows:

protected void setUp(  ) throws Exception {
    this.emptyPanel = new PersonEditorPanel(  );

    this.tanner = new Person("Tanner", "Burke");
    this.tannerPanel = new PersonEditorPanel(  );
    this.tannerPanel.setPerson(this.tanner);

    getTestFrame().getContentPane(  ).add(this.tannerPanel,
        BorderLayout.CENTER);
               getTestFrame().pack(  );
               getTestFrame().show(  );
}

This takes advantage of the JFrame provided by our base class, SwingTestCase