adding test

Author: benwtrent

server/src/test/java/org/elasticsearch/index/codec/vectors/IVFVectorsFormatTests.java

@@ -13,13 +13,25 @@
 import org.apache.lucene.codecs.Codec;
 import org.apache.lucene.codecs.FilterCodec;
 import org.apache.lucene.codecs.KnnVectorsFormat;
+import org.apache.lucene.codecs.KnnVectorsReader;
+import org.apache.lucene.codecs.perfield.PerFieldKnnVectorsFormat;
+import org.apache.lucene.document.Document;
+import org.apache.lucene.document.KnnFloatVectorField;
+import org.apache.lucene.index.CodecReader;
+import org.apache.lucene.index.DirectoryReader;
+import org.apache.lucene.index.IndexReader;
+import org.apache.lucene.index.IndexWriter;
+import org.apache.lucene.index.LeafReader;
 import org.apache.lucene.index.VectorEncoding;
 import org.apache.lucene.index.VectorSimilarityFunction;
+import org.apache.lucene.store.Directory;
 import org.apache.lucene.tests.index.BaseKnnVectorsFormatTestCase;
 import org.apache.lucene.tests.util.TestUtil;
 import org.elasticsearch.common.logging.LogConfigurator;
+import org.elasticsearch.index.codec.vectors.reflect.OffHeapByteSizeUtils;
 import org.junit.Before;
 
+import java.io.IOException;
 import java.util.List;
 import java.util.Locale;
 
@@ -94,4 +106,26 @@ public void testLimits() {
         expectThrows(IllegalArgumentException.class, () -> new IVFVectorsFormat(MIN_VECTORS_PER_CLUSTER - 1));
         expectThrows(IllegalArgumentException.class, () -> new IVFVectorsFormat(MAX_VECTORS_PER_CLUSTER + 1));
     }
+
+    public void testSimpleOffHeapSize() throws IOException {
+        float[] vector = randomVector(random().nextInt(12, 500));
+        try (Directory dir = newDirectory(); IndexWriter w = new IndexWriter(dir, newIndexWriterConfig())) {
+            Document doc = new Document();
+            doc.add(new KnnFloatVectorField("f", vector, VectorSimilarityFunction.EUCLIDEAN));
+            w.addDocument(doc);
+            w.commit();
+            try (IndexReader reader = DirectoryReader.open(w)) {
+                LeafReader r = getOnlyLeafReader(reader);
+                if (r instanceof CodecReader codecReader) {
+                    KnnVectorsReader knnVectorsReader = codecReader.getVectorReader();
+                    if (knnVectorsReader instanceof PerFieldKnnVectorsFormat.FieldsReader fieldsReader) {
+                        knnVectorsReader = fieldsReader.getFieldReader("f");
+                    }
+                    var fieldInfo = r.getFieldInfos().fieldInfo("f");
+                    var offHeap = OffHeapByteSizeUtils.getOffHeapByteSize(knnVectorsReader, fieldInfo);
+                    assertEquals(0, offHeap.size());
+                }
+            }
+        }
+    }
 }