How to get started: testing Java Swing GUI with AssertJ Swing

While developing a Java desktop application with Swing, I encountered the need to test the UI directly, and not just the underlying controller/model classes via unit tests.

This answer (on "What is the best testing tool for Swing-based applications?") suggested using FEST, which is unfortunately discontinued. However, there are a few projects that continued from where FEST left of. One in particular (mentioned in this answer) caught my attention, as I used it before in unit tests: AssertJ.

Apparently there is AssertJ Swing, which is based on FEST and offers some easy to use ways of writing your Swing UI tests. But still, getting to an initial/working setup is cumbersome as it's hard to say where to start.

How do I create a minimal test setup for the following example UI, consisting of only two classes?

Constraints: Java SE, Swing UI, Maven Project, JUnit

public class MainApp {

    /**
     * Run me, to use the app yourself.
     *
     * @param args ignored
     */
    public static void main(String[] args) {
        MainApp.showWindow().setSize(600, 600);
    }

    /**
     * Internal standard method to initialize the view, returning the main JFrame (also to be used in automated tests).
     *
     * @return initialized JFrame instance
     */
    public static MainWindow showWindow() {
        MainWindow mainWindow = new MainWindow();
        mainWindow.setVisible(true);
        return mainWindow;
    }
}

public class MainWindow extends JFrame {

    public MainWindow() {
        super("MainWindow");
        this.setContentPane(this.createContentPane());
    }

    private JPanel createContentPane() {
        JTextArea centerArea = new JTextArea();
        centerArea.setName("Center-Area");
        centerArea.setEditable(false);
        JButton northButton = this.createButton("North", centerArea);
        JButton southButton = this.createButton("South", centerArea);
        JPanel contentPane = new JPanel(new BorderLayout());
        contentPane.add(centerArea);
        contentPane.add(northButton, BorderLayout.NORTH);
        contentPane.add(southButton, BorderLayout.SOUTH);
        return contentPane;
    }

    private JButton createButton(final String text, final JTextArea centerArea) {
        JButton button = new JButton(text);
        button.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent event) {
                centerArea.setText(centerArea.getText() + text + ", ");
            }
        });
        return button;
    }
}

I'm aware that the question itself is very broad, therefore I provide an answer myself - show-casing this particular example.

TL;DR: the example project can be found on GitHub.

Assuming this is a maven project, you'll firstly need to add at least two dependencies:

A unit test framework (e.g. here junit – but could also use testng)
The matching AssertJ Swing library (e.g. here assertj-swing-junit)

It could look like this (in your pom.xml:

<dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.12</version>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>org.assertj</groupId>
    <artifactId>assertj-swing-junit</artifactId>
    <version>1.2.0</version>
    <scope>test</scope>
</dependency>

Secondly, I usually go for one base test class to separate most of the test setup from the actual tests:

/**
 * Base class for all my UI tests taking care of the basic setup.
 */
public class AbstractUiTest extends AssertJSwingTestCaseTemplate {

    /**
     * The main entry point for any tests: the wrapped MainWindow.
     */
    protected FrameFixture frame;

    /**
     * Installs a {@link FailOnThreadViolationRepaintManager} to catch violations of Swing threading rules.
     */
    @BeforeClass
    public static final void setUpOnce() {
        // avoid UI test execution in a headless environment (e.g. when building in CI environment like Jenkins or TravisCI)
        Assume.assumeFalse("Automated UI Test cannot be executed in headless environment", GraphicsEnvironment.isHeadless());
        FailOnThreadViolationRepaintManager.install();
    }

    /**
     * Sets up this test's fixture, starting from creation of a new <code>{@link Robot}</code>.
     *
     * @see #setUpRobot()
     * @see #onSetUp()
     */
    @Before
    public final void setUp() {
        // call provided AssertJSwingTestCaseTemplate.setUpRobot()
        this.setUpRobot();
        // initialize the graphical user interface
        MainWindow mainWindow = GuiActionRunner.execute(new GuiQuery<MainWindow>() {

            @Override
            protected MainWindow executeInEDT() throws Exception {
                return MainApp.showWindow();
            }
        });
        this.frame = new FrameFixture(this.robot(), mainWindow);
        this.frame.show();
        this.frame.resizeTo(new Dimension(600, 600));
        onSetUp();
    }

    /**
     * Subclasses that need to set up their own test fixtures in this method. Called as <strong>last action</strong> during {@link #setUp()}.
     */
    protected void onSetUp() {
        // default: everything is already set up
    }

    /*****************************************************************************************
     * Here you could insert further helper methods, e.g. frequently used component matchers *
     *****************************************************************************************/

    /**
     * Cleans up any resources used in this test. After calling <code>{@link #onTearDown()}</code>, this method cleans up resources used by this
     * test's <code>{@link Robot}</code>.
     *
     * @see #cleanUp()
     * @see #onTearDown()
     */
    @After
    public final void tearDown() {
        try {
            onTearDown();
            this.frame = null;
        } finally {
            cleanUp();
        }
    }

    /**
     * Subclasses that need to clean up resources can do so in this method. Called as <strong>first action</strong> during {@link #tearDown()}.
     */
    protected void onTearDown() {
        // default: nothing more to tear down
    }
}

The actual test class could look like this then:

public class MainWindowTest extends AbstractUiTest {

    private JButtonFixture northButtonFixture;
    private JButtonFixture southButtonFixture;

    @Override
    protected void onSetUp() {
        this.northButtonFixture = this.frame.button(JButtonMatcher.withText("North"));
        this.southButtonFixture = this.frame.button(JButtonMatcher.withText("South"));
    }

    @Test
    public void testWithDifferingComponentMatchers() {
        // use JTextComponentMatcher.any() as there is only one text input
        this.frame.textBox(JTextComponentMatcher.any()).requireVisible().requireEnabled().requireNotEditable().requireEmpty();
        this.northButtonFixture.requireVisible().requireEnabled().click();
        // use value assigned in MainWindow class via JTextArea.setName("Center-Area") to identify component here
        this.frame.textBox("Center-Area").requireText("North, ");

        this.southButtonFixture.requireVisible().requireEnabled().click();
        // write our own matcher
        JTextComponentFixture centerArea = this.frame.textBox(new GenericTypeMatcher(JTextArea.class, true) {
            @Override
            protected boolean isMatching(Component component) {
                return true;
            }
        });
        centerArea.requireVisible().requireEnabled().requireText("North, South, ");
    }

    @Override
    protected void onTearDown() {
        this.northButtonFixture = null;
        this.southButtonFixture = null;
    }
}

Once you have such a basic setup in your project, you might want to look into the various kinds of component matcher there are and potentially introduce a couple setName() calls on various of your components you want to test, in order to make your life a bit easier.

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