test: Replace OldIndexBackwardsCompatibilityIT#testOldClusterStates with a full cluster restart qa test

OldIndexBackwardsCompatibilityIT#testOldClusterStates tested whether global and index metadata could be read from data directory,
 this can also be tested in full cluster qa test that checks cluster state via api.

 Relates to #24939

Author: martijnvg

core/src/test/java/org/elasticsearch/VersionTests.java

@@ -352,4 +352,12 @@ public boolean isCompatible(Version left, Version right) {
         return result;
     }
 
+    // This exists because 5.1.0 was never released due to a mistake in the release process.
+    // This verifies that we never declare the version as "released" accidentally.
+    // It would never pass qa tests later on, but those come very far in the build and this is quick to check now.
+    public void testUnreleasedVersion() {
+        Version VERSION_5_1_0_UNRELEASED = Version.fromString("5.1.0");
+        VersionTests.assertUnknownVersion(VERSION_5_1_0_UNRELEASED);
+    }
+
 }

core/src/test/java/org/elasticsearch/bwcompat/OldIndexBackwardsCompatibilityIT.java

@@ -296,6 +296,48 @@ public void testAliasWithBadName() throws Exception {
         }
     }
 
+    public void testClusterState() throws Exception {
+        if (runningAgainstOldCluster) {
+            XContentBuilder mappingsAndSettings = jsonBuilder();
+            mappingsAndSettings.startObject();
+            mappingsAndSettings.field("template", index);
+            {
+                mappingsAndSettings.startObject("settings");
+                mappingsAndSettings.field("number_of_shards", 1);
+                mappingsAndSettings.field("number_of_replicas", 0);
+                mappingsAndSettings.endObject();
+            }
+            mappingsAndSettings.endObject();
+            client().performRequest("PUT", "/_template/template_1", Collections.emptyMap(),
+                new StringEntity(mappingsAndSettings.string(), ContentType.APPLICATION_JSON));
+            client().performRequest("PUT", "/" + index);
+        }
+
+        // verifying if we can still read some properties from cluster state api:
+        Map<String, Object> clusterState = toMap(client().performRequest("GET", "/_cluster/state"));
+
+        // Check some global properties:
+        String clusterName = (String) clusterState.get("cluster_name");
+        assertEquals("full-cluster-restart", clusterName);
+        String numberOfShards = (String) XContentMapValues.extractValue(
+            "metadata.templates.template_1.settings.index.number_of_shards", clusterState);
+        assertEquals("1", numberOfShards);
+        String numberOfReplicas = (String) XContentMapValues.extractValue(
+            "metadata.templates.template_1.settings.index.number_of_replicas", clusterState);
+        assertEquals("0", numberOfReplicas);
+
+        // Check some index properties:
+        numberOfShards = (String) XContentMapValues.extractValue("metadata.indices." + index +
+            ".settings.index.number_of_shards", clusterState);
+        assertEquals("1", numberOfShards);
+        numberOfReplicas = (String) XContentMapValues.extractValue("metadata.indices." + index +
+                ".settings.index.number_of_replicas", clusterState);
+        assertEquals("0", numberOfReplicas);
+        Version version = Version.fromId(Integer.valueOf((String) XContentMapValues.extractValue("metadata.indices." + index +
+            ".settings.index.version.created", clusterState)));
+        assertEquals(oldClusterVersion, version);
+
+    }
 
     void assertBasicSearchWorks(int count) throws IOException {
         logger.info("--> testing basic search");

qa/full-cluster-restart/src/test/java/org/elasticsearch/upgrades/FullClusterRestartIT.java

@@ -21,19 +21,14 @@
 
 import org.apache.logging.log4j.Logger;
 import org.apache.lucene.index.IndexWriter;
-import org.apache.lucene.util.TestUtil;
 import org.elasticsearch.Version;
 import org.elasticsearch.cluster.metadata.IndexMetaData;
 import org.elasticsearch.cluster.routing.allocation.decider.ThrottlingAllocationDecider;
-import org.elasticsearch.common.io.FileSystemUtils;
 import org.elasticsearch.common.settings.Settings;
-import org.elasticsearch.common.util.IndexFolderUpgrader;
 import org.elasticsearch.common.xcontent.NamedXContentRegistry;
-import org.elasticsearch.env.NodeEnvironment;
 import org.elasticsearch.index.MergePolicyConfig;
 
 import java.io.IOException;
-import java.io.InputStream;
 import java.nio.file.DirectoryStream;
 import java.nio.file.FileVisitResult;
 import java.nio.file.Files;
@@ -74,32 +69,6 @@ public static Settings getSettings() {
             .build();
     }
 
-    public static void upgradeIndexFolder(InternalTestCluster cluster, String nodeName) throws Exception {
-        final NodeEnvironment nodeEnvironment = cluster.getInstance(NodeEnvironment.class, nodeName);
-        IndexFolderUpgrader.upgradeIndicesIfNeeded(Settings.EMPTY, nodeEnvironment);
-    }
-
-    public static void loadIndex(String indexName, String indexFile, Path unzipDir, Path bwcPath, Logger logger, Path... paths) throws
-        Exception {
-        Path unzipDataDir = unzipDir.resolve("data");
-
-        Path backwardsIndex = bwcPath.resolve(indexFile);
-        // decompress the index
-        try (InputStream stream = Files.newInputStream(backwardsIndex)) {
-            TestUtil.unzip(stream, unzipDir);
-        }
-
-        // check it is unique
-        assertTrue(Files.exists(unzipDataDir));
-        Path[] list = FileSystemUtils.files(unzipDataDir);
-        if (list.length != 1) {
-            throw new IllegalStateException("Backwards index must contain exactly one cluster");
-        }
-
-        final Path src = getIndexDir(logger, indexName, indexFile, list[0]);
-        copyIndex(logger, src, src.getFileName().toString(), paths);
-    }
-
     public static Path getIndexDir(
         final Logger logger,
         final String indexName,
@@ -166,8 +135,4 @@ public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IO
             }
         });
     }
-
-    public static Version extractVersion(String index) {
-        return Version.fromString(index.substring(index.indexOf('-') + 1, index.lastIndexOf('.')));
-    }
 }