Add failing test

Signed-off-by: Thomas Farr <[email protected]>

java-client/src/test/java/org/opensearch/client/opensearch/_types/aggregations/FilterAggregateTest.java

@@ -0,0 +1,21 @@
+/*
+ * 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._types.aggregations;
+
+import org.junit.Test;
+import org.opensearch.client.opensearch.model.ModelTestCase;
+
+public class FilterAggregateTest extends ModelTestCase {
+    @Test
+    public void serializesNestedAggregates() {
+        String json = "{\"sum#l2_result\":{\"value\":1.0},\"doc_count\":1}";
+        FilterAggregate aggregate = fromJson(json, FilterAggregate._DESERIALIZER);
+        assertEquals(json, toJson(aggregate));
+    }
+}