Spotted one time in our CI headful test run:

SliderTooltipNPETest > testSliderTooltipNPE() FAILED
    org.opentest4j.AssertionFailedError: Timeout: Timeout waiting for tooltip to display ==> expected: <true> but was: <false>
        at app//org.junit.jupiter.api.AssertionFailureBuilder.build(AssertionFailureBuilder.java:151)
        at app//org.junit.jupiter.api.AssertionFailureBuilder.buildAndThrow(AssertionFailureBuilder.java:132)
        at app//org.junit.jupiter.api.AssertTrue.failNotTrue(AssertTrue.java:63)
        at app//org.junit.jupiter.api.AssertTrue.assertTrue(AssertTrue.java:36)
        at app//org.junit.jupiter.api.Assertions.assertTrue(Assertions.java:214)
        at app//test.util.Util.waitForLatch(Util.java:331)
        at app//test.robot.javafx.scene.SliderTooltipNPETest.dragSliderAfterTooltipDisplayed(SliderTooltipNPETest.java:99)
        at app//test.robot.javafx.scene.SliderTooltipNPETest.testSliderTooltipNPE(SliderTooltipNPETest.java:74)