[TEST] Wait for async LDAP search to finish (#81197)

LDAP SDK has a race condition where closing a connection while an async
search is still executing could lead to a Timer thread being orphaned.
See: pingidentity/ldapsdk#120 This commit
changes SearchGroupsResolverInMemoryTests so that it waits for the
pending async search to complete (or timeout) before returning. This
ensures that when the close the connection the Timer thread is cancelled
(and stays cancelled). Resolves: #80305

x-pack/plugin/security/src/test/java/org/elasticsearch/xpack/security/authc/ldap/SearchGroupsResolverInMemoryTests.java

@@ -31,12 +31,14 @@
 
 import java.util.List;
 import java.util.concurrent.ExecutionException;
+import java.util.concurrent.TimeUnit;
 
 import static org.elasticsearch.xpack.core.security.authc.RealmSettings.getFullSettingKey;
 import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.instanceOf;
 import static org.hamcrest.Matchers.is;
 import static org.hamcrest.Matchers.iterableWithSize;
+import static org.hamcrest.Matchers.lessThanOrEqualTo;
 
 public class SearchGroupsResolverInMemoryTests extends LdapTestCase {
 
@@ -77,6 +79,10 @@ public void testSearchTimeoutIsFailure() throws Exception {
             assertThat(((LDAPException) cause).getResultCode(), is(ResultCode.TIMEOUT));
         } finally {
             ldapServers[0].setProcessingDelayMillis(0);
+
+            // Wait for the async search to complete or timeout.
+            // Without this, we might trigger an orphaned thread - see https://github.com/pingidentity/ldapsdk/issues/120
+            assertBusy(() -> assertThat(connection.getActiveOperationCount(), lessThanOrEqualTo(0)), 2000, TimeUnit.MILLISECONDS);
         }
     }