[TEST] Force flush to ensure multiple segments.

Relates to #35333

x-pack/plugin/ccr/src/test/java/org/elasticsearch/xpack/ccr/action/ShardChangesTests.java

@@ -6,6 +6,7 @@
 package org.elasticsearch.xpack.ccr.action;
 
 import org.elasticsearch.ElasticsearchException;
+import org.elasticsearch.action.admin.indices.flush.FlushRequest;
 import org.elasticsearch.action.admin.indices.forcemerge.ForceMergeRequest;
 import org.elasticsearch.action.admin.indices.refresh.RefreshRequest;
 import org.elasticsearch.action.admin.indices.stats.ShardStats;
@@ -99,6 +100,7 @@ public class ShardChangesTests extends ESSingleNodeTestCase {
         for (int i = 0; i < 32; i++) {
             client().prepareIndex("index", "_doc", "1").setSource("{}", XContentType.JSON).get();
             client().prepareDelete("index", "_doc", "1").get();
+            client().admin().indices().flush(new FlushRequest("index").force(true)).actionGet();
         }
         client().admin().indices().refresh(new RefreshRequest("index")).actionGet();
         ForceMergeRequest forceMergeRequest = new ForceMergeRequest("index");