sint: Refactor SimpleResultSyncPoint to use Void

The existing 'return type' of the class is Boolean. That, however, is effectively unused: the only two usages are modified in this class, and is unreachable code (as an exception would have been thrown).

smack-integration-test/src/main/java/org/igniterealtime/smack/inttest/util/SimpleResultSyncPoint.java

@@ -18,10 +18,10 @@
 
 import org.junit.jupiter.api.Assertions;
 
-public class SimpleResultSyncPoint extends ResultSyncPoint<Boolean, Exception> {
+public class SimpleResultSyncPoint extends ResultSyncPoint<Void, Exception> {
 
     public void signal() {
-        signal(Boolean.TRUE);
+        signal((Void) null);
     }
 
     public void signalFailure() {

smack-integration-test/src/main/java/org/jivesoftware/smack/roster/LowLevelRosterIntegrationTest.java

@@ -63,10 +63,7 @@ public void presenceUnavailable(FullJid jid, Presence presence) {
         // conOne.
         conTwo.disconnect();
 
-        Boolean result = offlineTriggered.waitForResult(timeout);
-        if (!result) {
-            throw new Exception("presenceUnavailable() was not called");
-        }
+        SimpleResultSyncPoint.assertSuccess(offlineTriggered, timeout, "presenceUnavailable() was not called");
     }
 
 }

smack-integration-test/src/main/java/org/jivesoftware/smack/roster/RosterIntegrationTest.java

@@ -16,8 +16,6 @@
  */
 package org.jivesoftware.smack.roster;
 
-import static org.junit.jupiter.api.Assertions.assertTrue;
-
 import java.util.Collection;
 import java.util.concurrent.TimeoutException;
 
@@ -101,7 +99,7 @@ private void checkIfAddedAndSubscribed(Collection<Jid> addresses) {
         try {
             rosterOne.createItemAndRequestSubscription(conTwo.getUser().asBareJid(), conTwosRosterName, null);
 
-            assertTrue(addedAndSubscribed.waitForResult(2 * connection.getReplyTimeout()));
+            SimpleResultSyncPoint.assertSuccess(addedAndSubscribed, 2 * connection.getReplyTimeout(), "Did not receive expected roster item.");
         }
         finally {
             rosterTwo.removeSubscribeListener(subscribeListener);