public void Test__Get_Fail() { // Arrange var source = new EntityB { Name2 = "A" }; var multiTypeItems = new MultiTypeBinderBuilder <Key>() .WithType <EntityA>(opt1 => opt1 .WithProperty(x => x.Name1, Key.Name) .FinalizeType()) .WithType <EntityB>(opt1 => opt1 .WithProperty(x => x.Name2, Key.Name) .FinalizeType()) .Build() .Map(new List <object> { source }); // Act, Assert Assert.Throws <Exception>(() => multiTypeItems.First()[Key.RandomKey]); }