Queue.clearLeftItems to fix AbstractProjectTest.testGetBuildAfterGC test failure after 84a2593.

core/src/main/java/hudson/model/Queue.java

@@ -92,10 +92,6 @@ import java.util.Set;
 import java.util.Timer;
 import java.util.TreeSet;
 import java.util.Map.Entry;
-import java.util.concurrent.BlockingQueue;
-import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.ConcurrentMap;
-import java.util.concurrent.LinkedBlockingQueue;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.Future;
@@ -748,6 +744,15 @@ public class Queue extends ResourceController implements Saveable {
         return Collections.unmodifiableCollection(leftItems.asMap().values());
     }
 
+    /**
+     * Immediately clear the {@link #getLeftItems} cache.
+     * Useful for tests which need to verify that no links to a build remain.
+     * @since 1.519
+     */
+    public void clearLeftItems() {
+        leftItems.invalidateAll();
+    }
+
     /**
      * Gets all items that are in the queue but not blocked
      *