YARN-4901. QueueMetrics needs to be cleared before MockRM is initialized. Contributed by Peter Bacsko.

(cherry picked from commit 002dcc4ebf79bbaa5e603565640d8289991d781f)
(cherry picked from commit 69dc329acc0174b133e8b68f16b3e894329a6fd0)
(cherry picked from commit 67cf1f94cd321761d676c5c9a8a07913fc3c2a70)

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/MockRM.java

@@ -32,6 +32,7 @@ import java.util.Map;
 import java.util.Set;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.io.DataOutputBuffer;
+import org.apache.hadoop.metrics2.lib.DefaultMetricsSystem;
 import org.apache.hadoop.security.Credentials;
 import org.apache.hadoop.security.UserGroupInformation;
 import org.apache.hadoop.security.token.Token;
@@ -96,6 +97,7 @@ import org.apache.hadoop.yarn.server.resourcemanager.rmnode.RMNodeEventType;
 import org.apache.hadoop.yarn.server.resourcemanager.rmnode.RMNodeImpl;
 import org.apache.hadoop.yarn.server.resourcemanager.rmnode.RMNodeStartedEvent;
 import org.apache.hadoop.yarn.server.resourcemanager.scheduler.AbstractYarnScheduler;
+import org.apache.hadoop.yarn.server.resourcemanager.scheduler.QueueMetrics;
 import org.apache.hadoop.yarn.server.resourcemanager.scheduler.SchedulerApplication;
 import org.apache.hadoop.yarn.server.resourcemanager.scheduler.SchedulerApplicationAttempt;
 import org.apache.hadoop.yarn.server.resourcemanager.scheduler.SchedulerNode;
@@ -153,6 +155,9 @@ public class MockRM extends ResourceManager {
   public MockRM(Configuration conf, RMStateStore store,
       boolean useNullRMNodeLabelsManager, boolean useRealElector) {
     super();
+    // Clear metrics to avoid possible interference between tests
+    DefaultMetricsSystem.shutdown();
+    QueueMetrics.clearQueueMetrics();
     if (conf.getBoolean(TestResourceUtils.TEST_CONF_RESET_RESOURCE_TYPES,
         true)) {
       ResourceUtils.resetResourceTypes(conf);