[fix][test] Fix flaky LeaderElectionServiceTest and PersistentDispatcherFailoverConsumerTest (#25498)

Author: lhotari

pulsar-broker/src/test/java/org/apache/pulsar/broker/loadbalance/LeaderElectionServiceTest.java

@@ -80,13 +80,16 @@ public void anErrorShouldBeThrowBeforeLeaderElected() throws PulsarServerExcepti
         config.setMetadataStoreUrl("zk:127.0.0.1:" + bkEnsemble.getZookeeperPort());
         @Cleanup
         PulsarService pulsar = spyWithClassAndConstructorArgs(MockPulsarService.class, config);
-        pulsar.start();
 
         // mock pulsar.getLeaderElectionService() in a thread safe way
+        // This must be set up before start() to avoid UnfinishedStubbingException
+        // caused by background threads interacting with the spy during stubbing setup.
         AtomicReference<LeaderElectionService> leaderElectionServiceReference = new AtomicReference<>();
         Mockito.doAnswer(invocation -> leaderElectionServiceReference.get())
                 .when(pulsar).getLeaderElectionService();
 
+        pulsar.start();
+
         // broker and webService is started, but leaderElectionService not ready
         final String tenant = "elect";
         final String namespace = "ns";

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

@@ -112,6 +112,7 @@ public void setup() throws Exception {
         svcConfig.setClusterName("pulsar-cluster");
         svcConfig.setSystemTopicEnabled(false);
         svcConfig.setTopicLevelPoliciesEnabled(false);
+        svcConfig.setActiveConsumerFailoverDelayTimeMillis(0);
         pulsarTestContext = PulsarTestContext.builderForNonStartableContext()
                 .config(svcConfig)
                 .spyByDefault()