8252825: Add automated test for fix done in JDK-8218479

Reviewed-by: serb, prr

test/jdk/javax/swing/JTextPane/TestJTextPaneBackgroundColor.java

@@ -0,0 +1,140 @@
+/*
+ * Copyright (c) 2020, 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.
+ *
+ * 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.
+ */
+
+/*
+ * @test
+ * @requires (os.family == "linux")
+ * @key headful
+ * @bug 8218479
+ * @summary Tests JTextPane background color
+ * @run main TestJTextPaneBackgroundColor
+ */
+
+import javax.swing.JFrame;
+import javax.swing.JPanel;
+import javax.swing.JTextPane;
+import javax.swing.SwingUtilities;
+import javax.swing.UIManager;
+import javax.swing.UnsupportedLookAndFeelException;
+import java.awt.BorderLayout;
+import java.awt.Color;
+import java.awt.Component;
+import java.awt.Point;
+import java.awt.Rectangle;
+import java.awt.Robot;
+
+public class TestJTextPaneBackgroundColor {
+    private static JFrame frame;
+    private static JTextPane textPane;
+    private static Point point;
+    private static Rectangle rect;
+    private static Robot robot;
+    private static final String GTK_LAF_CLASS = "GTKLookAndFeel";
+
+    private static void blockTillDisplayed(Component comp) {
+        Point p = null;
+        while (p == null) {
+            try {
+                p = comp.getLocationOnScreen();
+            } catch (IllegalStateException e) {
+                try {
+                    Thread.sleep(500);
+                } catch (InterruptedException ie) {
+                }
+            }
+        }
+    }
+
+    public static void main(String[] args) throws Exception {
+        if (!System.getProperty("os.name").startsWith("Linux")) {
+            System.out.println("This test is meant for Linux platform only");
+            return;
+        }
+
+        for (UIManager.LookAndFeelInfo lookAndFeelInfo :
+                UIManager.getInstalledLookAndFeels()) {
+            if (lookAndFeelInfo.getClassName().contains(GTK_LAF_CLASS)) {
+                try {
+                    UIManager.setLookAndFeel(lookAndFeelInfo.getClassName());
+                } catch (final UnsupportedLookAndFeelException ignored) {
+                    System.out.println("GTK L&F could not be set, so this " +
+                            "test can not be run in this scenario ");
+                    return;
+                }
+            }
+        }
+
+        robot = new Robot();
+        robot.setAutoDelay(100);
+
+        try {
+            SwingUtilities.invokeAndWait(new Runnable() {
+                public void run() {
+                    JPanel panel = new JPanel();
+                    textPane = new JTextPane();
+                    textPane.setText("             ");
+                    panel.add(textPane, BorderLayout.CENTER);
+                    frame = new JFrame("TestJTextPaneBackgroundColor");
+                    frame.add(panel);
+                    frame.setSize(200, 200);
+                    frame.setAlwaysOnTop(true);
+                    frame.setLocationRelativeTo(null);
+                    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
+                    frame.setVisible(true);
+                }
+            });
+
+            robot.waitForIdle();
+            robot.delay(500);
+
+            blockTillDisplayed(textPane);
+            SwingUtilities.invokeAndWait(() -> {
+                point = textPane.getLocationOnScreen();
+                rect = textPane.getBounds();
+            });
+            robot.waitForIdle();
+            robot.delay(500);
+
+            Color textpaneBackgroundColor = robot
+                    .getPixelColor(point.x+rect.width/2, point.y+rect.height/2);
+            robot.waitForIdle();
+            robot.delay(500);
+
+            Color panelColor = robot
+                    .getPixelColor(point.x-rect.width/2, point.y+rect.height/2);
+            robot.waitForIdle();
+            robot.delay(500);
+
+            System.out.println(textpaneBackgroundColor);
+            System.out.println(panelColor);
+            if (textpaneBackgroundColor.equals(panelColor)) {
+                throw new RuntimeException("The expected background color for " +
+                        "TextPane was not found");
+            }
+        } finally {
+            if (frame != null) {
+                SwingUtilities.invokeAndWait(frame::dispose);
+            }
+        }
+    }
+}