Add cluster stats rolling version upgrade ITs.

Signed-off-by: Swetha Guptha <gupthasg@amazon.com>

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

@@ -0,0 +1,67 @@
+/*
+ * 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.Version;
+import org.opensearch.client.Request;
+import org.opensearch.client.Response;
+
+import java.io.IOException;
+import java.util.Collections;
+import java.util.List;
+import java.util.Map;
+
+public class ClusterStatsIT extends AbstractRollingTestCase {
+
+    private final List<String> nodeStatsMetrics = List.of("os", "process", "jvm", "fs", "plugins", "ingest", "network_types", "discovery_types", "packaging_types");
+
+    private final List<String> indicesStatsMetrics = List.of("shards", "docs", "store", "fielddata", "query_cache", "completion", "segments", "analysis", "mappings");
+
+    public void testClusterStats() throws IOException {
+        Response response = client().performRequest(new Request("GET", "/_cluster/stats"));
+        validateClusterStatsWithFilterResponse(response, nodeStatsMetrics, indicesStatsMetrics);
+        if (AbstractRollingTestCase.UPGRADE_FROM_VERSION.onOrAfter(Version.V_3_0_0) || (
+            CLUSTER_TYPE == ClusterType.UPGRADED && Version.CURRENT.onOrAfter(Version.V_3_0_0))) {
+            response = client().performRequest(new Request("GET", "/_cluster/stats/os/nodes/_all"));
+            validateClusterStatsWithFilterResponse(response, List.of("os"), Collections.emptyList());
+            response = client().performRequest(new Request("GET", "/_cluster/stats/indices/mappings/nodes/_all"));
+            validateClusterStatsWithFilterResponse(response, Collections.emptyList(), List.of("mappings"));
+            response = client().performRequest(new Request("GET", "/_cluster/stats/os,indices/mappings/nodes/_all"));
+            validateClusterStatsWithFilterResponse(response, List.of("os"), List.of("mappings"));
+        }
+    }
+
+    private void validateClusterStatsWithFilterResponse(Response response, List<String> requestedNodesStatsMetrics, List<String> requestedIndicesStatsMetrics) throws IOException {
+        assertEquals(200, response.getStatusLine().getStatusCode());
+        Map<String, Object> entity = entityAsMap(response);
+        if (requestedNodesStatsMetrics != null && !requestedNodesStatsMetrics.isEmpty()) {
+            assertTrue(entity.containsKey("nodes"));
+            Map<?, ?> nodesStats = (Map<?, ?>) entity.get("nodes");
+            for (String metric : nodeStatsMetrics) {
+                if (requestedNodesStatsMetrics.contains(metric)) {
+                    assertTrue(nodesStats.containsKey(metric));
+                } else {
+                    assertFalse(nodesStats.containsKey(metric));
+                }
+            }
+        }
+
+        if (requestedIndicesStatsMetrics != null && !requestedIndicesStatsMetrics.isEmpty()) {
+            assertTrue(entity.containsKey("indices"));
+            Map<?, ?> indicesStats = (Map<?, ?>) entity.get("indices");
+            for (String metric : indicesStatsMetrics) {
+                if (requestedIndicesStatsMetrics.contains(metric)) {
+                    assertTrue(indicesStats.containsKey(metric));
+                } else {
+                    assertFalse(indicesStats.containsKey(metric));
+                }
+            }
+        }
+    }
+}