Headless UI Testing with TestFX and JavaFX 8

JavaFX is a great UI toolkit. TestFX is a great library for testing the user interfaces written in JavaFX. Writing graphical tests with TestFX is simple and fast, but one challenge remains when you build your software using a headless build machine: how can you perform your UI tests in headless mode during your build?

Luckily, JavaFX 8 Update 20 will contain Monocle, which should allow us to run these headless tests.

First analysis using the latest beta of JDK 8u20 indicates that these tests are feasible, but require some changes in the TestFX library. We used a simple standalone JavaFX application for which we wrote a basic TestFX test class. We ran this test using the following command line options:

-Dglass.platform=Monocle
-Dmonocle.platform=Headless
-Dprism.order=sw

Unfortunately, this was not enough to make the test work. So we took a deeper look at the inner workings of TestFX and found that a working solution required the following changes:

1. refactor a part of the TestFX code such that different implementations of the org.loadui.testfx.framework.robot.ScreenRobot interface can be used. This allowed us to make test use an other robot implementation, in this case an adapter for MonocleRobot. The current TestFX implementation relies on java.awt.Robot, which uses the system event queue to move the system cursor. This, of course, does not integrate with Monocle in headless mode.

2. implement a ScreenRobot adapter for MonocleRobot. MonocleRobot is in internal package and thus not available via public API. In order to obtain an instance of this class, we had to call:

   java Platform.runLater(() -> { robot = com.sun.glass.ui.Application.GetApplication().createRobot(); ... });

This setup gave us a green test eventually. :-)