IconifyTest consistently fails on Ubuntu 16.04. It works on Mac and Windows, and on newer versions of Ubuntu (works on 20.04).

$ gradle --info -PFULL_TEST=true -PUSE_ROBOT=true cleanTest :systemTests:test --tests IconifyTest

test.robot.javafx.stage.IconifyTest > canIconifyDecoratedStage FAILED
    junit.framework.AssertionFailedError: expected:rgba(255,0,0,255) but was:rgba(113,35,105,255)
        at test.robot.testharness.VisualTestBase.assertColorEquals(VisualTestBase.java:179)
        at test.robot.javafx.stage.IconifyTest.lambda$canIconifyStage$4(IconifyTest.java:97)

test.robot.javafx.stage.IconifyTest > canIconifyUndecoratedStage FAILED
    junit.framework.AssertionFailedError: expected:rgba(255,0,0,255) but was:rgba(113,35,105,255)
        at test.robot.testharness.VisualTestBase.assertColorEquals(VisualTestBase.java:179)
        at test.robot.javafx.stage.IconifyTest.lambda$canIconifyStage$4(IconifyTest.java:97)

test.robot.javafx.stage.IconifyTest > canIconifyTransparentStage FAILED
    junit.framework.AssertionFailedError: expected:rgba(255,0,0,255) but was:rgba(0,255,0,255)
        at test.robot.testharness.VisualTestBase.assertColorEquals(VisualTestBase.java:179)
        at test.robot.javafx.stage.IconifyTest.lambda$canIconifyStage$4(IconifyTest.java:97)

test.robot.javafx.stage.IconifyTest > canIconifyNonResizableStage FAILED
    junit.framework.AssertionFailedError: expected:rgba(255,0,0,255) but was:rgba(113,35,105,255)
        at test.robot.testharness.VisualTestBase.assertColorEquals(VisualTestBase.java:179)
        at test.robot.javafx.stage.IconifyTest.lambda$canIconifyStage$4(IconifyTest.java:97)