How can I unit test EventHandler function?

Question

according to example in https://learn.microsoft.com/en-us/dotnet/api/system.windows.input.mousebuttoneventargs?view=net-5.0
how can I unit test this function

  private void MouseButtonDownHandler(object sender, MouseButtonEventArgs e)  
  {  
      Control src = e.Source as Control;  

      if (src != null)  
      {  
          switch (e.ChangedButton)  
          {  
              case MouseButton.Left:  
                  src.Background = Brushes.Green;  
                  break;  
              case MouseButton.Middle:  
                  src.Background = Brushes.Red;  
                  break;  
              case MouseButton.Right:  
                  src.Background = Brushes.Yellow;  
                  break;  
              case MouseButton.XButton1:  
                  src.Background = Brushes.Brown;  
                  break;  
              case MouseButton.XButton2:  
                  src.Background = Brushes.Purple;  
                  break;  
              default:  
                  break;  
          }  
      }  
  }

Answer 1

To test the logic, maybe move the logic to separate functions or classes or projects and test them. For example:

private void MouseButtonEventArgs( object sender, MouseButtonEventArgs e )
{
    Control src = e.Source as Control;
    if( src != null )
    {
        var b = MyLogic.GetBrush( e.ChangedButton );
        if( b != null ) src.Background = b;
    }
}

. . .
public class MyLogic
{
    public static Brush GetBrush( MouseButton changedButton )
    {
        switch( changedButton )
        {
        case MouseButton.Left:
            return Brushes.Green;
        case MouseButton.Middle:
            return Brushes.Red;
        case MouseButton.Right:
            return Brushes.Yellow;
        case MouseButton.XButton1:
            return Brushes.Brown;
        case MouseButton.XButton2:
            return Brushes.Purple;
        default:
            return null;
        }
    }
}
. . .
[TestClass]
public class MyTest
{
    [TestMethod]
    public void MyTest1( )
    {
        Assert.AreEqual( Brushes.Brown, MyLogic.GetBrush( MouseButton.XButton1 ) );
        // etc.
        // . . .

    }
}