Integration test: Fix race condition in CoreTest

Motivation
----------
MockConfigProvider had a race condition where the initial
ClusterConfig could be populated by a subsequent call to
accept(BucketConfig) *before* the initial config was processed,
resulting in redundant calls to Node.add/RemoveService().

This would normally be fine, since those methods are idempotent.
However, it violated the test assertion that they are called
exactly once.

Modifications
-------------
Don't publish the initial empty config; the tests don't depend on it.

Subsequent publications are implicitly serialized because the tests
verify the previous config was applied before telliing the mock config
provider to accept a new one.

Change-Id: Iab2ede125e801b6b35855a7bf1c10c106ee31d20
Reviewed-on: https://review.couchbase.org/c/couchbase-jvm-clients/+/212828
Tested-by: Build Bot <[email protected]>
Reviewed-by: David Nault <[email protected]>

core-io/src/test/java/com/couchbase/client/core/CoreTest.java

@@ -48,7 +48,6 @@
 import java.util.Optional;
 
 import static com.couchbase.client.test.Util.readResource;
-import static java.util.concurrent.TimeUnit.MILLISECONDS;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyInt;
@@ -103,18 +102,12 @@ private static class MockConfigProvider {
         configs.tryEmitComplete().orThrow();
         return Mono.empty();
       });
-
-      configs.tryEmitNext(clusterConfig).orThrow();
     }
 
     public void accept(BucketConfig bucketConfig) throws InterruptedException {
       clusterConfig.setBucketConfig(bucketConfig);
       logger.info("Emitting config {}", clusterConfig.allNodeAddresses());
       configs.tryEmitNext(clusterConfig).orThrow();
-
-      // A sleep after emitting the config prevents it intermittently
-      // emitting the config twice, for reasons that are unclear.
-      MILLISECONDS.sleep(500);
     }
   }
 
@@ -123,7 +116,6 @@ public void accept(BucketConfig bucketConfig) throws InterruptedException {
    * the difference in services and nodes is enabled.
    */
   @Test
-  @SuppressWarnings({"unchecked"})
   void addNodesAndServicesOnNewConfig() throws Exception {
     MockConfigProvider mockConfigProvider = new MockConfigProvider();
 
@@ -222,7 +214,6 @@ void configureMock(Node mock, String id, String ip, int port) {
   }
 
   @Test
-  @SuppressWarnings("unchecked")
   void addServicesOnNewConfig() throws Exception {
     MockConfigProvider mockConfigProvider = new MockConfigProvider();
 
@@ -307,7 +298,6 @@ protected Node createNode(final NodeIdentifier target) {
   }
 
   @Test
-  @SuppressWarnings("unchecked")
   void removeNodesAndServicesOnNewConfig() throws Exception {
     MockConfigProvider mockConfigProvider = new MockConfigProvider();
 
@@ -377,7 +367,6 @@ protected Node createNode(final NodeIdentifier target) {
   }
 
   @Test
-  @SuppressWarnings("unchecked")
   void removesNodeIfNotPresentInConfigAnymore() throws Exception {
     MockConfigProvider mockConfigProvider = new MockConfigProvider();
 
@@ -450,7 +439,6 @@ protected Node createNode(final NodeIdentifier target) {
    * the node is identified by a tuple of hostname and manager port, and this should work.
    */
   @Test
-  @SuppressWarnings("unchecked")
   void addsSecondNodeIfBothSameHostname() throws Exception {
     MockConfigProvider mockConfigProvider = new MockConfigProvider();