Creates TestUtilCleanupRule based on TestUtil

In #3029 it
was suggested to add a rule, this is the rule. It still need to be
applied to the test

TODO: Apply this to test

Author: vogella

tests/org.eclipse.ui.editors.tests/src/org/eclipse/ui/editors/tests/TestUtilCleanupRule.java

@@ -0,0 +1,65 @@
+package org.eclipse.ui.editors.tests;
+
+import java.util.concurrent.TimeUnit;
+
+import org.junit.Assert;
+import org.junit.rules.ExternalResource;
+
+import org.eclipse.swt.widgets.Display;
+
+import org.eclipse.core.runtime.jobs.Job;
+
+/**
+ * JUnit 4 rule to clean up state that can otherwise leak through SWT between
+ * tests.
+ */
+public class TestUtilCleanupRule extends ExternalResource {
+    @Override
+    protected void after() {
+        // Ensure that the Thread.interrupted() flag didn't leak.
+        Assert.assertFalse("The main thread should not be interrupted at the end of a test", Thread.interrupted());
+        // Wait for any outstanding jobs to finish. Protect against deadlock by terminating the wait after a timeout.
+        boolean timedOut = waitForJobs(0, TimeUnit.MINUTES.toMillis(3));
+        Assert.assertFalse("Some Job did not terminate at the end of the test", timedOut);
+        // Wait for any pending *syncExec calls to finish
+        runEventLoop();
+        // Ensure that the Thread.interrupted() flag didn't leak.
+        Assert.assertFalse("The main thread should not be interrupted at the end of a test", Thread.interrupted());
+    }
+
+    private static void runEventLoop() {
+        Display display = Display.getCurrent();
+        if (display != null && !display.isDisposed()) {
+            while (display.readAndDispatch()) {
+                // Keep pumping events until the queue is empty
+            }
+        }
+    }
+
+    private static boolean waitForJobs(long minTimeMs, long maxTimeMs) {
+        if (maxTimeMs < minTimeMs) {
+            throw new IllegalArgumentException("Max time is smaller as min time!");
+        }
+        final long start = System.currentTimeMillis();
+        while (System.currentTimeMillis() - start < minTimeMs) {
+            runEventLoop();
+            try {
+                Thread.sleep(100);
+            } catch (InterruptedException e) {
+                // Uninterruptable
+            }
+        }
+        while (!Job.getJobManager().isIdle()) {
+            if (System.currentTimeMillis() - start >= maxTimeMs) {
+                return true;
+            }
+            runEventLoop();
+            try {
+                Thread.sleep(100);
+            } catch (InterruptedException e) {
+                // Uninterruptable
+            }
+        }
+        return false;
+    }
+}