test: provide additional to deserialize parent aggregation

CHANGELOG.md

@@ -25,6 +25,7 @@ This section is for maintaining a changelog for all breaking changes for the cli
 
 ### Fixed
 - Fix version and build ([#254](https://github.com/opensearch-project/opensearch-java/pull/254))
+- Deserialize aggregation containing a parent aggregation ([#706](https://github.com/opensearch-project/opensearch-java/pull/706))
 
 ### Security
 

java-client/src/test/java/org/opensearch/client/opensearch/core/AggregateResponseTest.java

@@ -0,0 +1,51 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.client.opensearch.core;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import java.io.StringReader;
+import org.junit.Test;
+import org.opensearch.client.opensearch._types.aggregations.Aggregate;
+import org.opensearch.client.opensearch.model.ModelTestCase;
+
+public class AggregateResponseTest extends ModelTestCase {
+
+    @Test
+    public void shouldCreateParentAggregate() {
+        // given
+        final var aggregate = Aggregate.of((b) -> b.parent((p) -> p.docCount(789L)));
+
+        // when
+        final var parentAggregate = aggregate.parent();
+
+        // then
+        assertEquals(parentAggregate._aggregateKind(), Aggregate.Kind.Parent);
+        assertEquals(parentAggregate.docCount(), 789L);
+    }
+
+    @Test
+    public void shouldDeserializeParentAggregate() throws JsonProcessingException {
+        // given
+        final var parentAggreationJson = "{\"took\": 3,\"timed_out\": false,"
+            + "\"_shards\": {\"total\": 1,\"successful\": 1,\"skipped\": 0,\"failed\": 0},"
+            + "\"hits\": {\"total\": {\"value\": 0,\"relation\": \"eq\"},\"hits\": []},"
+            + "\"aggregations\": {\"parent#foo\": {\"doc_count\": 123456}}}";
+        final var parser = mapper.jsonProvider().createParser(new StringReader(parentAggreationJson));
+
+        // when
+        final var response = SearchResponse._DESERIALIZER.deserialize(parser, mapper);
+
+        // then
+        final var aggregations = response.aggregations();
+        assertFalse(aggregations.isEmpty());
+        assertTrue(aggregations.containsKey("foo"));
+        assertEquals(aggregations.get("foo").parent()._aggregateKind(), Aggregate.Kind.Parent);
+        assertEquals(aggregations.get("foo").parent().docCount(), 123456L);
+    }
+}