Added a bwc test

Signed-off-by: Shivansh Arora <[email protected]>

qa/rolling-upgrade/src/test/java/org/opensearch/upgrades/ClusterStateIT.java

@@ -0,0 +1,37 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.upgrades;
+
+import org.opensearch.client.Request;
+import org.opensearch.client.Response;
+
+import java.util.Map;
+
+public class ClusterStateIT extends AbstractRollingTestCase{
+    public void testTemplateMetadataUpgrades() throws Exception {
+        if (CLUSTER_TYPE == ClusterType.OLD) {
+            String templateName = "my_template";
+            Request putIndexTemplate = new Request("PUT", "_template/" + templateName);
+            putIndexTemplate.setJsonEntity("{\"index_patterns\": [\"pattern-1\", \"log-*\"]}");
+            client().performRequest(putIndexTemplate);
+            verifyTemplateMetadataInClusterState();
+        } else {
+            verifyTemplateMetadataInClusterState();
+        }
+    }
+
+    @SuppressWarnings("unchecked")
+    private static void verifyTemplateMetadataInClusterState() throws Exception {
+        Request request = new Request("GET", "_cluster/state/metadata");
+        Response response = client().performRequest(request);
+        assertOK(response);
+        Map<String, Object> metadata = (Map<String, Object>) entityAsMap(response).get("metadata");
+        assertNotNull(metadata.get("templates"));
+    }
+}