HDFS-16552. Fix NPE for TestBlockManager (#4210)

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/blockmanagement/TestBlockManager.java

@@ -854,6 +854,7 @@ public class TestBlockManager {
 
   @Test
   public void testSkipReconstructionWithManyBusyNodes() {
+    NameNode.initMetrics(new Configuration(), HdfsServerConstants.NamenodeRole.NAMENODE);
     long blockId = -9223372036854775776L; // real ec block id
     // RS-3-2 EC policy
     ErasureCodingPolicy ecPolicy =
@@ -899,6 +900,7 @@ public class TestBlockManager {
 
   @Test
   public void testSkipReconstructionWithManyBusyNodes2() {
+    NameNode.initMetrics(new Configuration(), HdfsServerConstants.NamenodeRole.NAMENODE);
     long blockId = -9223372036854775776L; // real ec block id
     // RS-3-2 EC policy
     ErasureCodingPolicy ecPolicy =