8351357: Add canary system test checking if Stage receives focus on show

tests/system/src/test/java/test/robot/javafx/stage/StageFocusTest.java

@@ -0,0 +1,131 @@
+/*
+ * Copyright (c) 2025, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package test.robot.javafx.stage;
+
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+
+import javafx.application.Application;
+import javafx.application.Platform;
+import javafx.scene.Group;
+import javafx.scene.Scene;
+import javafx.scene.input.KeyCode;
+import javafx.scene.paint.Color;
+import javafx.scene.robot.Robot;
+import javafx.stage.Stage;
+import javafx.stage.WindowEvent;
+import test.util.Util;
+import test.robot.testharness.VisualTestBase;
+
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+
+public class StageFocusTest extends VisualTestBase {
+
+    static CountDownLatch startupLatch;
+    static CountDownLatch eventReceivedLatch;
+
+    static final int STAGE_SIZE = 200;
+
+    static final int STAGE_X = 100;
+    static final int STAGE_Y = 100;
+
+    static final int TIMEOUT = 2000; // ms
+    static final double TOLERANCE = 0.07;
+
+    private Stage theStage = null;
+
+    @BeforeAll
+    public static void setupOnce() throws Exception {
+        startupLatch = new CountDownLatch(1);
+        eventReceivedLatch = new CountDownLatch(1);
+    }
+
+    /**
+     * Checks whether Stage is actually shown when calling show()
+     *
+     * Meant as a "canary" test of sorts to ensure other tests relying on
+     * Stage being actually shown and on foreground work fine.
+     */
+    @Test
+    public void testStageHasFocusAfterShow() throws InterruptedException {
+        Util.runAndWait(() -> {
+            theStage = getStage(false);
+
+            Group root = new Group();
+            Scene scene = new Scene(root, STAGE_SIZE, STAGE_SIZE);
+            scene.setFill(Color.LIGHTGREEN);
+            scene.setOnKeyPressed(e -> {
+                if (e.getCode() == KeyCode.A) {
+                    eventReceivedLatch.countDown();
+                }
+            });
+
+            theStage.setScene(scene);
+            theStage.addEventHandler(WindowEvent.WINDOW_SHOWN, e -> {
+                Platform.runLater(() -> {
+                    theStage.setX(STAGE_X);
+                    theStage.setY(STAGE_Y);
+                    startupLatch.countDown();
+                });
+            });
+            theStage.show();
+        });
+
+        assertTrue(startupLatch.await(TIMEOUT, TimeUnit.MILLISECONDS), "Timeout waiting for test stage to be shown");
+
+        // check if isFocused returns true
+        assertTrue(
+            theStage.isFocused(),
+            "Stage.isFocused() returned false! Stage does not have focus after showing. Some tests might fail because of this. " +
+            "If that is the case, try re-running the tests with '--no-daemon' flag in Gradle."
+        );
+
+        // give UI a bit of time to finish showing transition
+        // ex. on Windows above latch is set despite the UI still "animating" the show
+        sleep(500);
+
+        // check if window is on top
+        Util.runAndWait(() -> {
+            Color color = getColor(STAGE_SIZE / 2, STAGE_SIZE / 2);
+            assertColorEquals(Color.LIGHTGREEN, color, TOLERANCE);
+        });
+
+        // check if we actually have focus and key presses are registered by the app
+        Util.runAndWait(() -> {
+            getRobot().keyPress(KeyCode.A);
+        });
+        assertTrue(
+            eventReceivedLatch.await(TIMEOUT, TimeUnit.MILLISECONDS),
+            "Event received latch timed out! Stage most probably did not have focus after showing. Some tests might fail because of this. " +
+            "If that is the case, try re-running the tests with '--no-daemon' flag in Gradle."
+        );
+    }
+}