public void TestToHashtable()
 {
     var wrapper = new BsonDocumentWrapper(new BsonDocument { { "x", 1 }, { "y", 2 } });
     Assert.AreEqual(false, wrapper.IsMaterialized);
     var hashtable = wrapper.ToHashtable();
     Assert.AreEqual(true, wrapper.IsMaterialized);
     Assert.AreEqual(2, hashtable.Count);
     Assert.AreEqual(1, hashtable["x"]);
     Assert.AreEqual(2, hashtable["y"]);
 }