Use a parquet-backed index in CalcitePPLAggregationIT.testSimpleCount0

The test created an ad-hoc 'test' index with raw _doc PUTs. On the analytics-engine
route (tests.analytics.parquet_indices) that bare auto-created index is not
composite/parquet-backed, so it does not route through the analytics engine and the
test is not exercising the intended path. Switch to TEST_INDEX_BANK, which init()
loads via loadIndex (which injects the parquet settings when the flag is set, 7
docs), so the test is meaningful on both the v2/Calcite and analytics-engine paths.
Verified passing on both routes.

Diagnosis by Sandesh Kumar.

Signed-off-by: Kai Huang <ahkcs@amazon.com>

Author: ahkcs

integ-test/src/test/java/org/opensearch/sql/calcite/remote/CalcitePPLAggregationIT.java

@@ -25,7 +25,6 @@
 import java.util.List;
 import org.json.JSONObject;
 import org.junit.jupiter.api.Test;
-import org.opensearch.client.Request;
 import org.opensearch.sql.common.utils.StringUtils;
 import org.opensearch.sql.exception.SemanticCheckException;
 import org.opensearch.sql.ppl.PPLIntegTestCase;
@@ -52,16 +51,15 @@ public void init() throws Exception {
 
   @Test
   public void testSimpleCount0() throws IOException {
-    Request request1 = new Request("PUT", "/test/_doc/1?refresh=true");
-    request1.setJsonEntity("{\"name\": \"hello\", \"age\": 20}");
-    client().performRequest(request1);
-    Request request2 = new Request("PUT", "/test/_doc/2?refresh=true");
-    request2.setJsonEntity("{\"name\": \"world\", \"age\": 30}");
-    client().performRequest(request2);
-
-    JSONObject actual = executeQuery("source=test | stats count() as c");
+    // Use TEST_INDEX_BANK (loaded in init via loadIndex, 7 docs) rather than an ad-hoc index
+    // created with raw _doc PUTs. On the analytics-engine route a bare auto-created index is not
+    // composite/parquet-backed, so it does not route to the analytics engine; loadIndex injects the
+    // parquet settings when tests.analytics.parquet_indices is set, keeping this test meaningful on
+    // both engine paths.
+    JSONObject actual =
+        executeQuery(String.format("source=%s | stats count() as c", TEST_INDEX_BANK));
     verifySchema(actual, schema("c", "bigint"));
-    verifyDataRows(actual, rows(2));
+    verifyDataRows(actual, rows(7));
   }
 
   @Test