How do you unit test a JavaFX controller with JUnit

Question

What\'s the proper way of initializing the JavaFX runtime so you can unit test (with JUnit) controllers that make use of the concurrency facilities and Platform.runLat

Answer 1

Calling launch() from @BeforeClass is a correct approach. Just note that launch() doesn't return control to calling code. So you have to wrap it into new Thread(...).start().

A 7 years later update:

Use TestFX! It will take care of launching in a proper way. E.g. you can extend your test from a TestFX's ApplicaionTest class and just use the same code:

public class MyTest extends ApplicationTest {

@Override
public void start (Stage stage) throws Exception {
    FXMLLoader loader = new FXMLLoader(
            getClass().getResource("mypage.fxml"));
    stage.setScene(scene = new Scene(loader.load(), 300, 300));
    stage.show();
}

and write tests like that:

@Test
public void testBlueHasOnlyOneEntry() {
    clickOn("#tfSearch").write("blue");
    verifyThat("#labelCount", hasText("1"));
}

Answer 2

I found this to work,... but only after adding a Thread.sleep(500) after starting the JavaFX application thread. Presumably it takes some time to get the FX environment up and ready (about 200ms on my MacBook Pro retina)

@BeforeClass
public static void setUpClass() throws InterruptedException {
    // Initialise Java FX

    System.out.printf("About to launch FX App\n");
    Thread t = new Thread("JavaFX Init Thread") {
        public void run() {
            Application.launch(AsNonApp.class, new String[0]);
        }
    };
    t.setDaemon(true);
    t.start();
    System.out.printf("FX App thread started\n");
    Thread.sleep(500);
}