add Unit tests.

Author: hfutatzhanghb

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/router/RouterRpcClient.java

@@ -280,6 +280,15 @@ public ActiveNamenodeResolver getNamenodeResolver() {
     return this.namenodeResolver;
   }
 
+  /**
+   * Get the executor service used by invoking concurrent calls.
+   * @return
+   */
+  @VisibleForTesting
+  public ThreadPoolExecutor getExecutorService() {
+    return executorService;
+  }
+
   /**
    * Shutdown the client.
    */

hadoop-hdfs-project/hadoop-hdfs-rbf/src/test/java/org/apache/hadoop/hdfs/server/federation/router/TestRouterRpc.java

@@ -2426,4 +2426,9 @@ public void testCallerContextNotResetByAsyncHandler() throws IOException {
     // The audit log should not contain async:true.
     assertFalse(auditLog.getOutput().contains("async:true"));
   }
+
+  @Test
+  public void testConcurrentCallExecutorInitial() {
+    assertNotNull(router.getRouterRpcClient().getExecutorService());
+  }
 }

hadoop-hdfs-project/hadoop-hdfs-rbf/src/test/java/org/apache/hadoop/hdfs/server/federation/router/async/TestRouterAsyncRpc.java

@@ -36,6 +36,7 @@
 import static org.apache.hadoop.hdfs.server.federation.router.RBFConfigKeys.DFS_ROUTER_FAIRNESS_POLICY_CONTROLLER_CLASS;
 import static org.apache.hadoop.hdfs.server.federation.router.async.utils.AsyncUtil.syncReturn;
 import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
 
 /**
  * Testing the asynchronous RPC functionality of the router.
@@ -83,4 +84,9 @@ public void testgetGroupsForUser() throws Exception {
     assertArrayEquals(group, result);
   }
 
+  @Test
+  @Override
+  public void testConcurrentCallExecutorInitial() {
+    assertNull(rndRouter.getRouterRpcClient().getExecutorService());
+  }
 }

hadoop-hdfs-project/hadoop-hdfs-rbf/src/test/java/org/apache/hadoop/hdfs/server/federation/router/async/TestRouterAsyncRpcMultiDestination.java

@@ -34,6 +34,7 @@
 import static org.apache.hadoop.hdfs.server.federation.router.RBFConfigKeys.DFS_ROUTER_FAIRNESS_POLICY_CONTROLLER_CLASS;
 import static org.apache.hadoop.hdfs.server.federation.router.async.utils.AsyncUtil.syncReturn;
 import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
 
 /**
  * Testing the asynchronous RPC functionality of the router with multiple mounts.
@@ -70,4 +71,11 @@ public void testgetGroupsForUser() throws Exception {
     String[] result = syncReturn(String[].class);
     assertArrayEquals(group, result);
   }
+
+  @Test
+  @Override
+  public void testConcurrentCallExecutorInitial() {
+    MiniRouterDFSCluster.RouterContext rndRouter = super.getRouterContext();
+    assertNull(rndRouter.getRouterRpcClient().getExecutorService());
+  }
 }