Remove `ClusterStateSerializationTests` (#130877)

These tests do not seem valuable anymore, now that multi-project has
been merged some time ago. Additionally, creating objects for a cluster
state this way is tricky, as those objects might get new
features/fields, which would break serialization.

Closes #130872

muted-tests.yml

@@ -403,9 +403,6 @@ tests:
 - class: org.elasticsearch.backwards.MixedClusterClientYamlTestSuiteIT
   method: test {p0=mtermvectors/10_basic/Tests catching other exceptions per item}
   issue: https://github.com/elastic/elasticsearch/issues/122414
-- class: org.elasticsearch.cluster.ClusterStateSerializationTests
-  method: testSerializationPreMultiProject
-  issue: https://github.com/elastic/elasticsearch/issues/130872
 - class: org.elasticsearch.search.SearchWithRejectionsIT
   method: testOpenContextsAfterRejections
   issue: https://github.com/elastic/elasticsearch/issues/130821

server/src/test/java/org/elasticsearch/cluster/ClusterStateSerializationTests.java

@@ -1,85 +0,0 @@
-/*
- * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
- * or more contributor license agreements. Licensed under the "Elastic License
- * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
- * Public License v 1"; you may not use this file except in compliance with, at
- * your election, the "Elastic License 2.0", the "GNU Affero General Public
- * License v3.0 only", or the "Server Side Public License, v 1".
- */
-
-package org.elasticsearch.cluster;
-
-import org.elasticsearch.TransportVersion;
-import org.elasticsearch.TransportVersions;
-import org.elasticsearch.cluster.metadata.DataStreamTestHelper;
-import org.elasticsearch.cluster.metadata.Metadata;
-import org.elasticsearch.cluster.metadata.ProjectMetadata;
-import org.elasticsearch.cluster.node.DiscoveryNode;
-import org.elasticsearch.cluster.node.DiscoveryNodeUtils;
-import org.elasticsearch.cluster.node.DiscoveryNodes;
-import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
-import org.elasticsearch.core.Tuple;
-import org.elasticsearch.test.ESTestCase;
-import org.elasticsearch.test.MapMatcher;
-import org.elasticsearch.test.TransportVersionUtils;
-import org.elasticsearch.test.XContentTestUtils;
-import org.hamcrest.Matchers;
-
-import java.io.IOException;
-import java.util.List;
-import java.util.Set;
-
-public class ClusterStateSerializationTests extends ESTestCase {
-
-    public void testSerializationInCurrentVersion() throws IOException {
-        assertSerializationRoundTrip(TransportVersion.current());
-    }
-
-    public void testSerializationPreMultiProject() throws IOException {
-        assertSerializationRoundTrip(TransportVersionUtils.getPreviousVersion(TransportVersions.MULTI_PROJECT));
-    }
-
-    private void assertSerializationRoundTrip(TransportVersion transportVersion) throws IOException {
-        ClusterState original = randomClusterState(transportVersion);
-        DiscoveryNode node = original.nodes().getLocalNode();
-        assertThat(node, Matchers.notNullValue());
-
-        final ClusterState deserialized = ESTestCase.copyWriteable(
-            original,
-            new NamedWriteableRegistry(ClusterModule.getNamedWriteables()),
-            in -> ClusterState.readFrom(in, node),
-            transportVersion
-        );
-        assertEquivalent("For transport version: " + transportVersion, original, deserialized);
-    }
-
-    private void assertEquivalent(String context, ClusterState expected, ClusterState actual) throws IOException {
-        if (expected == actual) {
-            return;
-        }
-        // The simplest model we have for comparing equivalence is by comparing the XContent of the cluster state
-        var expectedJson = XContentTestUtils.convertToMap(expected);
-        var actualJson = XContentTestUtils.convertToMap(actual);
-        assertThat(context, actualJson, MapMatcher.matchesMap(expectedJson));
-    }
-
-    private ClusterState randomClusterState(TransportVersion transportVersion) {
-        final Set<String> datastreamNames = randomSet(0, 10, () -> randomAlphaOfLengthBetween(4, 18));
-        final List<Tuple<String, Integer>> datastreams = datastreamNames.stream()
-            .map(name -> new Tuple<>(name, randomIntBetween(1, 5)))
-            .toList();
-        final List<String> indices = List.copyOf(
-            randomSet(0, 10, () -> randomValueOtherThanMany(datastreamNames::contains, () -> randomAlphaOfLengthBetween(3, 12)))
-        );
-
-        final DiscoveryNodes.Builder nodes = DiscoveryNodes.builder();
-        do {
-            final String id = randomUUID();
-            nodes.add(DiscoveryNodeUtils.create(id));
-            nodes.localNodeId(id);
-        } while (randomBoolean());
-
-        ProjectMetadata project = DataStreamTestHelper.getProjectWithDataStreams(datastreams, indices);
-        return ClusterState.builder(ClusterName.DEFAULT).metadata(Metadata.builder().put(project)).nodes(nodes).build();
-    }
-}

server/src/test/java/org/elasticsearch/cluster/metadata/MetadataTests.java

@@ -10,6 +10,7 @@
 package org.elasticsearch.cluster.metadata;
 
 import org.elasticsearch.TransportVersion;
+import org.elasticsearch.TransportVersions;
 import org.elasticsearch.cluster.ClusterModule;
 import org.elasticsearch.cluster.Diff;
 import org.elasticsearch.cluster.coordination.CoordinationMetadata;
@@ -45,6 +46,7 @@ import org.elasticsearch.persistent.PersistentTasksExecutorRegistry;
 import org.elasticsearch.persistent.PersistentTasksService;
 import org.elasticsearch.test.AbstractChunkedSerializingTestCase;
 import org.elasticsearch.test.ESTestCase;
+import org.elasticsearch.test.TransportVersionUtils;
 import org.elasticsearch.test.index.IndexVersionUtils;
 import org.elasticsearch.test.rest.ObjectPath;
 import org.elasticsearch.threadpool.ThreadPool;
@@ -613,6 +615,17 @@ public class MetadataTests extends ESTestCase {
         }
     }
 
+    public void testUnableToSerializeNonDefaultProjectBeforeMultiProject() {
+        final var projectId = randomUniqueProjectId();
+        Metadata metadata = Metadata.builder().put(ProjectMetadata.builder(projectId)).build();
+
+        try (BytesStreamOutput output = new BytesStreamOutput()) {
+            output.setTransportVersion(TransportVersionUtils.getPreviousVersion(TransportVersions.MULTI_PROJECT));
+            var e = assertThrows(UnsupportedOperationException.class, () -> metadata.writeTo(output));
+            assertEquals("There is 1 project, but it has id [" + projectId + "] rather than default", e.getMessage());
+        }
+    }
+
     public void testGetNonExistingProjectThrows() {
         final List<ProjectMetadata> projects = IntStream.range(0, between(1, 3))
             .mapToObj(i -> randomProject(ProjectId.fromId("p_" + i), between(0, 5)))