[fix][test] Fix flaky test PersistentTopicTest.testGetReplicationClus…

…ters (apache#19421)

(cherry picked from commit 91c7ef7)

pulsar-broker/src/test/java/org/apache/pulsar/broker/service/PersistentTopicTest.java

@@ -544,7 +544,7 @@ public void testProducerOverwrite() throws Exception {
 
     private void testMaxProducers() throws Exception {
         PersistentTopic topic = new PersistentTopic(successTopicName, ledgerMock, brokerService);
-        topic.initialize();
+        topic.initialize().join();
         String role = "appid1";
         // 1. add producer1
         Producer producer = new Producer(topic, serverCnx, 1 /* producer id */, "prod-name1", role,
@@ -2320,7 +2320,7 @@ private ByteBuf getMessageWithMetadata(byte[] data) {
     @Test
     public void testGetReplicationClusters() throws Exception {
         PersistentTopic topic = new PersistentTopic(successTopicName, ledgerMock, brokerService);
-        topic.initialize();
+        topic.initialize().join();
         assertEquals(topic.getHierarchyTopicPolicies().getReplicationClusters().get(), Collections.emptyList());
 
         PulsarResources pulsarResources = spyWithClassAndConstructorArgs(PulsarResources.class, store, store);
@@ -2339,7 +2339,7 @@ public void testGetReplicationClusters() throws Exception {
         doReturn(policiesFuture).when(nsr).getPoliciesAsync(any());
 
         topic = new PersistentTopic(successTopicName, ledgerMock, brokerService);
-        topic.initialize();
+        topic.initialize().join();
         assertEquals(topic.getHierarchyTopicPolicies().getReplicationClusters().get(), namespaceClusters);
 
         TopicPoliciesService topicPoliciesService = mock(TopicPoliciesService.class);
@@ -2354,7 +2354,7 @@ public void testGetReplicationClusters() throws Exception {
         when(topicPoliciesService.getTopicPoliciesIfExists(any())).thenReturn(topicPolicies);
 
         topic = new PersistentTopic(successTopicName, ledgerMock, brokerService);
-        topic.initialize();
+        topic.initialize().join();
         assertEquals(topic.getHierarchyTopicPolicies().getReplicationClusters().get(), namespaceClusters);
     }
 }