assertThat(map.get("test"), instanceOf(DBRef.class));
DBObject mapValDBObject = new BasicDBObject();
mapValDBObject.put("_id", BigInteger.ONE);
DBRef dbRef = mock(DBRef.class);
when(dbRef.fetch()).thenReturn(mapValDBObject);
((DBObject) dbObject.get("map")).put("test", dbRef);
MapDBRef read = converter.read(MapDBRef.class, dbObject);