Bug 576655 - Use ResourceTracker in JUnit tests

The goal of this change is to automatically detect leaks in SWT
internal code such as leak in CTabFolder.setFont() that was fixed in
569752. Such errors happen rarely, but on the other hand, detecting
them is cheap, so it makes sense to detect.

I decided to enable tracking in 'AllNonBrowserTests' because it's often
chosen over 'AllTests'.

Also fixes some existing leaks in JUnit tests.

Change-Id: Ida9c2a0b31465546adedbe6bd1850d1d9ac618e7
Signed-off-by: Alexandr Miloslavskiy <alexandr.miloslavskiy@syntevo.com>
Reviewed-on: https://git.eclipse.org/r/c/platform/eclipse.platform.swt/+/186543
Tested-by: Platform Bot <platform-bot@eclipse.org>
Reviewed-by: Andrey Loskutov <loskutov@gmx.de>

Author: SyntevoAlex

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/AllNonBrowserTests.java

@@ -14,10 +14,16 @@
  *******************************************************************************/
 package org.eclipse.swt.tests.junit;
 
+import org.eclipse.swt.graphics.Resource;
+import org.junit.AfterClass;
+import org.junit.BeforeClass;
 import org.junit.runner.JUnitCore;
 import org.junit.runner.RunWith;
 import org.junit.runners.Suite;
 
+import java.util.ArrayList;
+import java.util.List;
+
 /**
  * Suite for running most SWT test cases (all except for browser tests).
  */
@@ -41,6 +47,50 @@
 		Test_org_eclipse_swt_accessibility_AccessibleEvent.class,
 		Test_org_eclipse_swt_accessibility_AccessibleTextEvent.class })
 public class AllNonBrowserTests {
+	private static List<Error> leakedResources;
+
+	@BeforeClass
+	public static void beforeClass() {
+		// Set up ResourceTracked to detect any leaks
+		leakedResources = new ArrayList<> ();
+		Resource.setNonDisposeHandler (error -> {
+			// Can't 'Assert.fail()' here, because Handler is called on
+			// some other thread and Exception will simply be ignored.
+			// Workaround: collect errors and report later.
+			leakedResources.add (error);
+		});
+	}
+
+	/*
+	 * It would be easier to understand if errors here were reported
+	 * through  a test and not through @AfterClass, but this is a
+	 * suite class and not a test class, so it can't have tests.
+	 */
+	@AfterClass
+	public static void afterClass() {
+		// Run GC in order do detect any outstanding leaks
+		System.gc ();
+		// And wait a bit to let Resource.ResourceTracker, that is
+		// queued to another thread, do its job. It is unfortunate that
+		// there is no simple better way to wait except waiting some
+		// fixed timeout.
+		try {
+			Thread.sleep (100);
+		} catch (InterruptedException e) {
+			// Just ignore
+		}
+
+		for (Error leak : leakedResources) {
+			// For some reason, printing to System.err in JUnit test has no effect
+			leak.printStackTrace (System.out);
+		}
+
+		if (0 != leakedResources.size ()) {
+			// In order to help tools to filter fail reason out of entire log, throw the first leak.
+			String hint = leakedResources.size () + " leaks found, the first is:";
+			throw new AssertionError(hint, leakedResources.get (0));
+		}
+	}
 
 	public static void main(String[] args) {
 		JUnitCore.main(AllNonBrowserTests.class.getName());

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_custom_StyledText_multiCaretsSelections.java

@@ -50,15 +50,18 @@ protected void failed(Throwable e, org.junit.runner.Description description) {
 
 	Shell shell;
 	StyledText text;
+	GC gc;
 
 	@Before
 	public void setUp() {
 		shell = new Shell();
 		text = new StyledText(shell, SWT.NULL);
+		gc = new GC(text);
 	}
 
 	@After
 	public void tearDown() {
+		gc.dispose();
 		shell.dispose();
 	}
 	@Test
@@ -184,7 +187,7 @@ private Event paintEvent() {
 		paintEvent.height = text.getSize().y;
 		paintEvent.widget = text;
 		paintEvent.type = SWT.Paint;
-		paintEvent.gc = new GC(text);
+		paintEvent.gc = gc;
 		return paintEvent;
 	}
 

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_graphics_Image.java

@@ -1116,6 +1116,11 @@ public void test_bug566545_efficientGrayscaleImage() {
 	ImageTestUtil.assertImagesEqual(imageDataIndexed, imageDataDirect);
 	ImageTestUtil.assertImagesEqual(imageIndexed.getImageData(), imageDirect.getImageData());
 	ImageTestUtil.assertImagesEqual(outImageIndexed.getImageData(), outImageDirect.getImageData());
+
+	imageIndexed.dispose();
+	imageDirect.dispose();
+	outImageIndexed.dispose();
+	outImageDirect.dispose();
 }
 
 }