在wpf

Question

XAML：

            <ListView   ItemsSource="{Binding Persons}">
                <ListView.View>
                    <GridView>
                        <GridViewColumn DisplayMemberBinding="{Binding Name}" Header="Name" />
                        <GridViewColumn DisplayMemberBinding="{Binding FirstName}" Header="FirstName" />
                        <GridViewColumn DisplayMemberBinding="{Binding Test}" Header="Test" />
                    </GridView>
                </ListView.View>
            </ListView>

CS：

    public ObservableCollection<Person> Persons { get; private set; }
    private string _test;

    public string Test
    {
        get { return _test; }
        set { _test = value; RaisePropertyChanged("Test"); }
    }
    public MainViewModel()
    {
        this.Persons = new ObservableCollection<Person>
        {
            new Person
            {
                Name = "Doe",
                FirstName = "John",
                DateOfBirth = new DateTime(1981, 9, 12)
            },
            new Person
            {
                Name = "Black",
                FirstName = "Jack",
                DateOfBirth = new DateTime(1950, 1, 15)
            }
        };
        Test = "TestTestTestTestTest";
    }

如何正确绑定值（Test）？ListView是UserControl的一部分，我试图绑定到下面的语法，但它仍然无效。

{Binding Test , RelativeSource={RelativeSource FindAncestor,  AncestorType={x:Type viewModel:MainViewModel}}}