Reinstate testLogsWarningPeriodicallyIfClusterNotFormed (#95416)

This test now works for atomic-register coordinators, with slightly
different assertions about the log messages.

Relates #95409

Author: DaveCTurner

server/src/test/java/org/elasticsearch/cluster/coordination/AtomicRegisterCoordinatorTests.java

@@ -65,9 +65,15 @@ public void testUnhealthyLeaderIsReplaced() {
     }
 
     @Override
-    @AwaitsFix(bugUrl = "ES-5645")
+    @TestLogging(
+        reason = "testing ClusterFormationFailureHelper logging",
+        value = "org.elasticsearch.cluster.coordination.ClusterFormationFailureHelper:WARN"
+    )
     public void testLogsWarningPeriodicallyIfClusterNotFormed() {
-        // All nodes have access to the register, therefore it's possible to form a single-node cluster
+        testLogsWarningPeriodicallyIfClusterNotFormed(
+            "master not discovered or elected yet, an election requires a node with id [",
+            nodeId -> "*have discovered possible quorum *" + nodeId + "*discovery will continue*"
+        );
     }
 
     @Override

server/src/test/java/org/elasticsearch/cluster/coordination/CoordinatorTests.java

@@ -54,6 +54,7 @@
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Function;
+import java.util.function.UnaryOperator;
 import java.util.stream.Collectors;
 
 import static java.util.Collections.emptyMap;
@@ -1602,6 +1603,13 @@ public void testClusterRecoversAfterExceptionDuringSerialization() {
         value = "org.elasticsearch.cluster.coordination.ClusterFormationFailureHelper:WARN"
     )
     public void testLogsWarningPeriodicallyIfClusterNotFormed() {
+        testLogsWarningPeriodicallyIfClusterNotFormed(
+            "master not discovered or elected yet, an election requires at least 2 nodes with ids from [",
+            nodeId -> "*have only discovered non-quorum *" + nodeId + "*discovery will continue*"
+        );
+    }
+
+    protected void testLogsWarningPeriodicallyIfClusterNotFormed(String expectedMessageStart, UnaryOperator<String> discoveryMessageFn) {
         final long warningDelayMillis;
         final Settings settings;
         if (randomBoolean()) {
@@ -1645,10 +1653,7 @@ public void testLogsWarningPeriodicallyIfClusterNotFormed() {
                         @Override
                         public void match(LogEvent event) {
                             final String message = event.getMessage().getFormattedMessage();
-                            assertThat(
-                                message,
-                                startsWith("master not discovered or elected yet, an election requires at least 2 nodes with ids from [")
-                            );
+                            assertThat(message, startsWith(expectedMessageStart));
 
                             final List<ClusterNode> matchingNodes = cluster.clusterNodes.stream()
                                 .filter(
@@ -1659,13 +1664,7 @@ public void match(LogEvent event) {
                                 .toList();
                             assertThat(matchingNodes, hasSize(1));
 
-                            assertTrue(
-                                message,
-                                Regex.simpleMatch(
-                                    "*have only discovered non-quorum *" + matchingNodes.get(0).toString() + "*discovery will continue*",
-                                    message
-                                )
-                            );
+                            assertTrue(message, Regex.simpleMatch(discoveryMessageFn.apply(matchingNodes.get(0).toString()), message));
 
                             nodesLogged.add(matchingNodes.get(0).getLocalNode());
                         }