JUnit Rule for JavaFX Controller Testing

Testing JavaFX controllers is relatively easy although you do have to jump through a couple of hoops. Firstly, JavaFX must be initialised and secondly JavaFX controls must only be mutated on the JavaFX thread created internally during initialisation. The JUnit rule below will setup JavaFX once and run all tests on the FX thread. All you need to do is create it as a field in your test case class and annotate it with @org.junit.Rule. You will need to be running JUnit 4.9 to use the rule API.

	import java.util.concurrent.CountDownLatch;
	import javax.swing.SwingUtilities;
	import javafx.application.Platform;
	import javafx.embed.swing.JFXPanel;
	import org.junit.Rule;
	import org.junit.rules.TestRule;
	import org.junit.runner.Description;
	import org.junit.runners.model.Statement;
	/**
	* A JUnit {@link Rule} for running tests on the JavaFX thread and performing
	* JavaFX initialisation. To include in your test case, add the following code:
	*
	* <pre>
	* {@literal @}Rule
	* public JavaFXThreadingRule jfxRule = new JavaFXThreadingRule();
	* </pre>
	*
	* @author Andy Till
	*
	*/
	public class JavaFXThreadingRule implements TestRule {
	/**
	* Flag for setting up the JavaFX, we only need to do this once for all tests.
	*/
	private static boolean jfxIsSetup;
	@Override
	public Statement apply(Statement statement, Description description) {
	return new OnJFXThreadStatement(statement);
	}
	private static class OnJFXThreadStatement extends Statement {
	private final Statement statement;
	public OnJFXThreadStatement(Statement aStatement) {
	statement = aStatement;
	}
	private Throwable rethrownException = null;
	@Override
	public void evaluate() throws Throwable {
	if(!jfxIsSetup) {
	setupJavaFX();
	jfxIsSetup = true;
	}
	final CountDownLatch countDownLatch = new CountDownLatch(1);
	Platform.runLater(new Runnable() {
	@Override
	public void run() {
	try {
	statement.evaluate();
	} catch (Throwable e) {
	rethrownException = e;
	}
	countDownLatch.countDown();
	}});
	countDownLatch.await();
	// if an exception was thrown by the statement during evaluation,
	// then re-throw it to fail the test
	if(rethrownException != null) {
	throw rethrownException;
	}
	}
	protected void setupJavaFX() throws InterruptedException {
	long timeMillis = System.currentTimeMillis();
	final CountDownLatch latch = new CountDownLatch(1);
	SwingUtilities.invokeLater(new Runnable() {
	public void run() {
	// initializes JavaFX environment
	new JFXPanel();
	latch.countDown();
	}
	});
	System.out.println("javafx initialising...");
	latch.await();
	System.out.println("javafx is initialised in " + (System.currentTimeMillis() - timeMillis) + "ms");
	}
	}
	}

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