public void TestDeepClone()
 {
     var wrapper = new BsonDocumentWrapper(new BsonDocument("x", 1));
     Assert.AreEqual(false, wrapper.IsMaterialized);
     var deepClone = wrapper.DeepClone();
     Assert.AreEqual(true, wrapper.IsMaterialized);
     Assert.IsInstanceOf<BsonDocument>(deepClone);
     Assert.AreEqual(wrapper, deepClone);
 }