[improve] [test] add end to end deduplication test.

pulsar-broker/src/main/java/org/apache/pulsar/broker/service/ServerCnx.java

@@ -3551,6 +3551,11 @@ public PulsarCommandSender getCommandSender() {
         return commandSender;
     }
 
+    @VisibleForTesting
+    public void setCommandSender(PulsarCommandSender commandSender) {
+        this.commandSender = commandSender;
+    }
+
     @Override
     public void execute(Runnable runnable) {
         ctx().channel().eventLoop().execute(runnable);