JavaFXThreadingRule.java

package be.raildelays.javafx.test;

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;

import javax.swing.*;
import java.lang.reflect.Method;
import java.net.URLClassLoader;
import java.util.concurrent.CountDownLatch;

/**
 * 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:
 * <p>
 * <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 loaded;

    @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 {
            CountDownLatch countDownLatch = new CountDownLatch(1);

            if (!loaded) {
                setupJavaFX();

                loaded = true;
            }

            Platform.runLater(() -> {
                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();
            CountDownLatch latch = new CountDownLatch(1);

            SwingUtilities.invokeLater(() -> {
                // 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");
        }

    }
}