test: make sure we don't flush during indexing the percolator queries

core/src/test/java/org/elasticsearch/index/percolator/PercolatorQueryCacheTests.java

@@ -125,6 +125,8 @@ public class PercolatorQueryCacheTests extends ESTestCase {
         IndexWriter indexWriter = new IndexWriter(
                 directory,
                 newIndexWriterConfig(new MockAnalyzer(random()))
+                        .setMergePolicy(NoMergePolicy.INSTANCE)
+                        .setMaxBufferedDocs(16)
         );
 
         boolean legacyFormat = randomBoolean();