It is a static method. You just need to implement a test method for JUnit using the method. What you want is to check whether it throws exception properly if something goes wrong. Also, you need to check if it can return what you want. That's all. Do you know how to use JUnit by the way?
For Each ctrl As Control In Me.Controls("pnlMainPanel").Controls
If ctrl.GetType Is GetType(System.Windows.Forms.Panel) Then
For Each subCtrl As Control In ctrl.Controls
If subCtrl.GetType Is GetType(System.Windows.Forms.TextBox) Then
If subCtrl.GetType Is ...