Fix ClusterRebalanceRoutingTests (#90110)

This test assumes that rebalancing will rebalance `test1` rather than
planning to rebalance `test2` once its primary has finished
initializing. By adding two more nodes we ensure that it plans to
rebalance both indices.

server/src/test/java/org/elasticsearch/cluster/routing/allocation/ClusterRebalanceRoutingTests.java

@@ -21,6 +21,7 @@ import org.elasticsearch.cluster.routing.RoutingTable;
 import org.elasticsearch.cluster.routing.ShardRouting;
 import org.elasticsearch.cluster.routing.UnassignedInfo;
 import org.elasticsearch.cluster.routing.allocation.decider.ClusterRebalanceAllocationDecider;
+import org.elasticsearch.common.collect.Iterators;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.test.gateway.TestGatewayAllocator;
 
@@ -63,7 +64,7 @@ public class ClusterRebalanceRoutingTests extends ESAllocationTestCase {
 
         logger.info("start two nodes");
         clusterState = ClusterState.builder(clusterState)
-            .nodes(DiscoveryNodes.builder().add(newNode("node1")).add(newNode("node2")))
+            .nodes(DiscoveryNodes.builder().add(newNode("node1")).add(newNode("node2")).localNodeId("node1").masterNodeId("node1"))
             .build();
         clusterState = strategy.reroute(clusterState, "reroute");
 
@@ -109,13 +110,16 @@ public class ClusterRebalanceRoutingTests extends ESAllocationTestCase {
             assertThat(clusterState.routingTable().index("test2").shard(i).replicaShards().get(0).state(), equalTo(UNASSIGNED));
         }
 
-        logger.info("now, start 1 more node, check that rebalancing will happen (for test1) because we set it to always");
-        clusterState = ClusterState.builder(clusterState).nodes(DiscoveryNodes.builder(clusterState.nodes()).add(newNode("node3"))).build();
+        logger.info("now, start 2 more nodes, check that rebalancing will happen (for test1) because we set it to always");
+        clusterState = ClusterState.builder(clusterState)
+            .nodes(DiscoveryNodes.builder(clusterState.nodes()).add(newNode("node3")).add(newNode("node4")))
+            .build();
         clusterState = strategy.reroute(clusterState, "reroute");
         RoutingNodes routingNodes = clusterState.getRoutingNodes();
 
-        assertThat(routingNodes.node("node3").size(), equalTo(1));
-        assertThat(routingNodes.node("node3").iterator().next().shardId().getIndex().getName(), equalTo("test1"));
+        final var newNodesIterator = Iterators.concat(routingNodes.node("node3").iterator(), routingNodes.node("node4").iterator());
+        assertThat(newNodesIterator.next().shardId().getIndex().getName(), equalTo("test1"));
+        assertFalse(newNodesIterator.hasNext());
     }
 
     public void testClusterPrimariesActive1() {