AutoCompleteBox.SelectedItem binding not working

Jun 27 at 2:11 PM
Hello,
I'm trying to bind my ViewModels selectedItem property to your AutoCompleteBox.SelectedItem property, but I can't get it to work, can you help me?
Here's my code;

MainWindow.xaml
<Window x:Class="Test.View.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:Test.View"
        xmlns:itk="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Input.Toolkit"
        xmlns:vm="clr-namespace:Test.ViewModel"
        mc:Ignorable="d"
        Title="MainWindow" Height="auto" Width="auto" d:DesignHeight="300" d:DesignWidth="300">
    <Window.Resources>
        <DataTemplate x:Key="testItemTemplate">
            <TextBlock Text="{Binding text}"/>
        </DataTemplate>
    </Window.Resources>
    <Window.DataContext>
        <vmTestViewModel/>
    </Window.DataContext>
    <StackPanel>
        <itk:AutoCompleteBox Width="150" Height="50" Text="{Binding text}" ItemsSource="{Binding items}" SelectedItem="{Binding selecteditem, Mode=TwoWay}" ValueMemberPath="text" ItemTemplate="{StaticResource testItemTemplate}"/>
        <TextBlock Text="{Binding selectedItem.text}"/>
        <TextBox/>
    </StackPanel>
</Window>
TestViewModel.cs
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Test.ViewModel
{
    public class TestViewModel
    {

        public IEnumerable<test> items { get; private set; }
        public TestViewModel()
        {
            items = new List<test>()
            {
                new test() { text= "hi" },
                new test() { text= "hi2" }
            };
        }

        public class test
        {
            public string text { get; set; }
        }

        public test selectedItem { get; set; }

    }
}
Only the binding for the list works, but not for the selectedItem, I don't understand that.