Create a custom DataGrid's ItemsSource - not working

I am trying to replicate the solution from Create a custom DataGrid's ItemsSource but my rows are not populating.

The columns appears with the correct headers, but no data in the grid.

Can anyone please tell me what I am doing wrong?

using System;
using System.Windows;
using System.ComponentModel;
using System.Collections.ObjectModel;
using System.Runtime.CompilerServices;

namespace WPFBindingDataGridTest2
{
    public partial class MainWindow : Window
    {
        public ObservableCollection<MyObject> myList { get; set; }

        public MainWindow()
        {
            InitializeComponent();
            this.DataContext = this;

            testClass = new ObservableCollection<TestClass>();
            testClass.Add(new TestClass(NameValue: "John"));
            testClass.Add(new TestClass(NameValue: "Frank"));
            testClass.Add(new TestClass(NameValue: "Sarah"));
            testClass.Add(new TestClass(NameValue: "David"));
        }
    }

    class TestClass : INotifyPropertyChanged
    {
        private string name;

        public TestClass(string NameValue)
        {
            this.Name = NameValue;
        }

        public String Name
        {
            get { return name; }
            set { this.name = value; NotifyPropertyChanged(); }
        }

        public event PropertyChangedEventHandler PropertyChanged;

        private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
        {
            if (this.PropertyChanged != null)
                this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

And the XAML...

<Grid>
    <DataGrid x:Name="dataGrid" ItemsSource="{Binding testClass}" AutoGenerateColumns="False">
        <DataGrid.Columns>
            <DataGridTextColumn Header="Name" Binding="{Binding Name}"/>
        </DataGrid.Columns>
    </DataGrid>
</Grid>

The error I am getting is

System.Windows.Data Error: 40 :  
BindingExpression path error:  
'testClass' property not found on 'object'''MainWindow' 
(Name='')'.BindingExpression:  
Path=testClass;  
DataItem='MainWindow' (Name='');  
target element is 'DataGrid' (Name='dataGrid');  
target property is 'ItemsSource' (type 'IEnumerable')

I feel like I am so close to this, but am just missing one thing.
Possible the data context is wrong?

when you assign DataContext, myList is null. When it is created later, property doesn't report about changing (via event)

quick fix is to change the order of operations:

public MainWindow()
{
    myList = new ObservableCollection<MyObject>
    {
      new MyObject() { MyID = "6222" },
      new MyObject() { MyID = "12" },
      new MyObject() { MyID = "666" }
    };
    this.DataContext = this;
    InitializeComponent();
}

also fix column binding (Binding="{Binding MyID}") or property name (MyId) because binding path should match property name

but I suggest to create a separate class (which implements INotifyPropertyChanged) with myList property, and use an instance of that class (view model) to set DataContext of a window.