Add uT

Signed-off-by: John Mazanec <[email protected]>

src/test/java/org/opensearch/knn/index/codec/KNN9120Codec/DerivedSourceStoredFieldsWriterTests.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.opensearch.knn.index.codec.KNN9120Codec;
+
+import lombok.SneakyThrows;
+import org.apache.lucene.codecs.StoredFieldsWriter;
+import org.apache.lucene.index.FieldInfo;
+import org.apache.lucene.util.BytesRef;
+import org.opensearch.common.io.stream.BytesStreamOutput;
+import org.opensearch.core.xcontent.MediaTypeRegistry;
+import org.opensearch.core.xcontent.XContentBuilder;
+import org.opensearch.knn.KNNTestCase;
+import org.opensearch.knn.index.codec.KNNCodecTestUtil;
+
+import java.util.List;
+import java.util.Map;
+
+import static org.mockito.Mockito.mock;
+
+public class DerivedSourceStoredFieldsWriterTests extends KNNTestCase {
+
+    @SneakyThrows
+    public void testWriteField() {
+        StoredFieldsWriter delegate = mock(StoredFieldsWriter.class);
+        FieldInfo fieldInfo = KNNCodecTestUtil.FieldInfoBuilder.builder("_source").build();
+        List<String> fields = List.of("test");
+
+        DerivedSourceStoredFieldsWriter derivedSourceStoredFieldsWriter = new DerivedSourceStoredFieldsWriter(delegate, fields);
+
+        Map<String, Object> source = Map.of("test", new float[] { 1.0f, 2.0f, 3.0f }, "text_field", "text_value");
+        BytesStreamOutput bStream = new BytesStreamOutput();
+        XContentBuilder builder = MediaTypeRegistry.contentBuilder(MediaTypeRegistry.JSON, bStream).map(source);
+        builder.close();
+        byte[] originalBytes = bStream.bytes().toBytesRef().bytes;
+        byte[] shiftedBytes = new byte[originalBytes.length + 2];
+        System.arraycopy(originalBytes, 0, shiftedBytes, 1, originalBytes.length);
+        derivedSourceStoredFieldsWriter.writeField(fieldInfo, new BytesRef(shiftedBytes, 1, originalBytes.length));
+    }
+}