Fix flaky test KNNJVectorTests.testJVectorKnnIndex_simpleCase (#305)

* Fix flaky test KNNJVectorTests.testJVectorKnnIndex_simpleCase

Signed-off-by: Medha Srinivasarao Srivatsa <medha.srivatsa@gmail.com>

* Fix indentation and update changelog

Signed-off-by: Medha Srinivasarao Srivatsa <medha.srivatsa@gmail.com>

* Apply suggestions from code review

Co-authored-by: Andriy Redko <drreta@gmail.com>
Signed-off-by: Andriy Redko <drreta@gmail.com>

---------

Signed-off-by: Medha Srinivasarao Srivatsa <medha.srivatsa@gmail.com>
Signed-off-by: Andriy Redko <drreta@gmail.com>
Co-authored-by: Andriy Redko <drreta@gmail.com>
(cherry picked from commit a181659)

Author: 2 people

src/test/java/org/opensearch/knn/index/codec/jvector/KNNJVectorTests.java

@@ -60,6 +60,7 @@ public void testJVectorKnnIndex_simpleCase() throws IOException {
         indexWriterConfig.setUseCompoundFile(false);
         indexWriterConfig.setCodec(getCodec());
         indexWriterConfig.setMergePolicy(new ForceMergesOnlyMergePolicy());
+        log.info("Max buffered docs: {}", indexWriterConfig.getMaxBufferedDocs());
         final Path indexPath = createTempDir();
         log.info("Index path: {}", indexPath);
         try (FSDirectory dir = FSDirectory.open(indexPath); IndexWriter w = new IndexWriter(dir, indexWriterConfig)) {
@@ -74,8 +75,12 @@ public void testJVectorKnnIndex_simpleCase() throws IOException {
             w.commit();
 
             try (IndexReader reader = DirectoryReader.open(w)) {
-                log.info("We should now have a single segment with 10 documents");
-                Assert.assertEquals(1, reader.getContext().leaves().size());
+                int expectedNumOfSegments = indexWriterConfig.getMaxBufferedDocs() < 0 ? 1
+                    : totalNumberOfDocs > indexWriterConfig.getMaxBufferedDocs()
+                        ? totalNumberOfDocs / indexWriterConfig.getMaxBufferedDocs() + 1
+                    : 1;
+                log.info("We should now have a {} segment(s) with 10 documents", expectedNumOfSegments);
+                Assert.assertEquals(expectedNumOfSegments, reader.getContext().leaves().size());
                 Assert.assertEquals(totalNumberOfDocs, reader.numDocs());
 
                 final Query filterQuery = new MatchAllDocsQuery();