Fixing DataStreamsUpgradeIT.testUpgradeDataStream when cluster major version is unchanged (#119786)

Author: masseyke

muted-tests.yml

@@ -247,9 +247,6 @@ tests:
 - class: org.elasticsearch.search.profile.dfs.DfsProfilerIT
   method: testProfileDfs
   issue: https://github.com/elastic/elasticsearch/issues/119711
-- class: org.elasticsearch.upgrades.DataStreamsUpgradeIT
-  method: testUpgradeDataStream
-  issue: https://github.com/elastic/elasticsearch/issues/119717
 - class: org.elasticsearch.xpack.esql.optimizer.LocalPhysicalPlanOptimizerTests
   method: testSingleMatchFunctionFilterPushdownWithStringValues {default}
   issue: https://github.com/elastic/elasticsearch/issues/119720

x-pack/qa/rolling-upgrade/src/test/java/org/elasticsearch/upgrades/DataStreamsUpgradeIT.java

@@ -281,18 +281,22 @@ private void upgradeDataStream(String dataStreamName, int numRolloversOnOldClust
             );
             assertOK(statusResponse);
             assertThat(statusResponseMap.get("complete"), equalTo(true));
-            // The number of rollovers that will have happened when we call reindex:
-            final int rolloversPerformedByReindex = explicitRolloverOnNewClusterCount == 0 ? 1 : 0;
             final int originalWriteIndex = 1;
-            assertThat(
-                statusResponseMap.get("total_indices_in_data_stream"),
-                equalTo(originalWriteIndex + numRolloversOnOldCluster + explicitRolloverOnNewClusterCount + rolloversPerformedByReindex)
-            );
             if (isOriginalClusterSameMajorVersionAsCurrent()) {
+                assertThat(
+                    statusResponseMap.get("total_indices_in_data_stream"),
+                    equalTo(originalWriteIndex + numRolloversOnOldCluster + explicitRolloverOnNewClusterCount)
+                );
                 // If the original cluster was the same as this one, we don't want any indices reindexed:
                 assertThat(statusResponseMap.get("total_indices_requiring_upgrade"), equalTo(0));
                 assertThat(statusResponseMap.get("successes"), equalTo(0));
             } else {
+                // The number of rollovers that will have happened when we call reindex:
+                final int rolloversPerformedByReindex = explicitRolloverOnNewClusterCount == 0 ? 1 : 0;
+                assertThat(
+                    statusResponseMap.get("total_indices_in_data_stream"),
+                    equalTo(originalWriteIndex + numRolloversOnOldCluster + explicitRolloverOnNewClusterCount + rolloversPerformedByReindex)
+                );
                 /*
                  * total_indices_requiring_upgrade is made up of: (the original write index) + numRolloversOnOldCluster. The number of
                  * rollovers on the upgraded cluster is irrelevant since those will not be reindexed.