how to test when headless?

[i-make-robots]

Hello, I hope you are well.

I hope this is the right area for this issue.

I've been up and down the assertj swing documentation and I don't see any mention of how to run headless unit tests. My specific case is that I want to test my JPanel interaction results. I tried the following:

public class PaperSettingsPanelTest extends AssertJSwingJUnitTestCase {
	private JPanelFixture panel;

	@Override
	protected void onSetUp() {
		PreferencesHelper.start();
		Translator.start();
		panel = new JPanelFixture(robot(),new PaperSettingsPanel(new Paper()));
	}

	@SuppressWarnings("unlikely-arg-type")
	@Test
	public void testLandscapeToPortrait() {
		panel.comboBox("size").selectItem(1);
		assert(panel.textBox("width.field").equals("1682"));
		assert(panel.textBox("height.field").equals("2378"));
		panel.comboBox("size").selectItem(1);
		panel.checkBox("landscape").click();
		assert(panel.textBox("width.field").equals("2378"));
		assert(panel.textBox("height.field").equals("1682"));
	}
}

and I get

java.lang.ExceptionInInitializerError
	at org.assertj.swing.monitor.WindowMonitor.instance(WindowMonitor.java:143)
	at org.assertj.swing.core.BasicRobot.<clinit>(BasicRobot.java:123)
	at org.assertj.swing.testing.AssertJSwingTestCaseTemplate.setUpRobot(AssertJSwingTestCaseTemplate.java:36)
	at org.assertj.swing.junit.testcase.AssertJSwingJUnitTestCase.setUp(AssertJSwingJUnitTestCase.java:48)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
	at java.base/java.lang.reflect.Method.invoke(Method.java:580)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
	at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:24)
	at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
	at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69)
	at com.intellij.rt.junit.IdeaTestRunner$Repeater$1.execute(IdeaTestRunner.java:38)
	at com.intellij.rt.execution.junit.TestsRepeater.repeat(TestsRepeater.java:11)
	at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:35)
	at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:232)
	at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:55)
Caused by: java.awt.HeadlessException
	at java.desktop/sun.java2d.HeadlessGraphicsEnvironment.getScreenDevices(HeadlessGraphicsEnvironment.java:52)
	at org.assertj.swing.util.RobotFactory.newRobotInLeftScreen(RobotFactory.java:52)
	at org.assertj.swing.monitor.WindowStatus.<init>(WindowStatus.java:57)
	at org.assertj.swing.monitor.WindowStatus.<init>(WindowStatus.java:50)
	at org.assertj.swing.monitor.WindowMonitor.<init>(WindowMonitor.java:60)
	at org.assertj.swing.monitor.WindowMonitor$SingletonLazyLoader$1.executeInEDT(WindowMonitor.java:151)
	at org.assertj.swing.monitor.WindowMonitor$SingletonLazyLoader$1.executeInEDT(WindowMonitor.java:148)
	at org.assertj.swing.edt.GuiQuery.run(GuiQuery.java:42)
	at java.desktop/java.awt.event.InvocationEvent.dispatch$$$capture(InvocationEvent.java:318)
	at java.desktop/java.awt.event.InvocationEvent.dispatch(InvocationEvent.java)
	at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:773)
	at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:720)
	at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:714)
	at java.base/java.security.AccessController.doPrivileged(AccessController.java:400)
	at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:87)
	at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:742)
	at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:203)
	at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:124)
	at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:113)
	at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:109)
	at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
	at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:90)
	at org.assertj.swing.edt.GuiActionRunner.execute(GuiActionRunner.java:98)
	at org.assertj.swing.monitor.WindowMonitor$SingletonLazyLoader.<clinit>(WindowMonitor.java:148)
	... 29 more


java.lang.NullPointerException: Cannot invoke "org.assertj.swing.core.Robot.cleanUp()" because "this.robot" is null

	at org.assertj.swing.testing.AssertJSwingTestCaseTemplate.cleanUp(AssertJSwingTestCaseTemplate.java:43)
	at org.assertj.swing.junit.testcase.AssertJSwingJUnitTestCase.tearDown(AssertJSwingJUnitTestCase.java:82)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
	at java.base/java.lang.reflect.Method.invoke(Method.java:580)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
	at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:33)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
	at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69)
	at com.intellij.rt.junit.IdeaTestRunner$Repeater$1.execute(IdeaTestRunner.java:38)
	at com.intellij.rt.execution.junit.TestsRepeater.repeat(TestsRepeater.java:11)
	at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:35)
	at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:232)
	at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:55)

This happens with both IntelliJ IDEA running the tests on my desktop (?!) and Maven lifecycle tests.

fwiw the project is https://github.com/MarginallyClever/Makelangelo-software and the test case is src/test/java/com/marginallyclever/makelangelo/paper/PaperSettingsPanelTest.java

Can someone please give me a hint how to do this right? I have a lot of panels that could use tests.