public void ToBuilder() { DynamicMessage.Builder builder = DynamicMessage.CreateBuilder(TestAllTypes.Descriptor); reflectionTester.SetAllFieldsViaReflection(builder); int unknownFieldNum = 9; ulong unknownFieldVal = 90; builder.SetUnknownFields(UnknownFieldSet.CreateBuilder() .AddField(unknownFieldNum, UnknownField.CreateBuilder().AddVarint(unknownFieldVal).Build()) .Build()); DynamicMessage message = builder.Build(); DynamicMessage derived = message.ToBuilder().Build(); reflectionTester.AssertAllFieldsSetViaReflection(derived); IList <ulong> values = derived.UnknownFields.FieldDictionary[unknownFieldNum].VarintList; Assert.AreEqual(1, values.Count); Assert.AreEqual(unknownFieldVal, values[0]); }