Creates an ID for a control that doesn't have one provided in the .aspx page. The tester using this method must algorithmically determine what number ASP.NET provided to the control. In other words, control number "3" turns into an ID of "ctl03" in ASP.NET 2.0 and "_ctl3" in ASP.NET 1.x.
A string that includes the control number and reflects the scheme ASP.NET uses for anonymous control.
AspControlTester Class | NUnit.Extensions.Asp.AspTester Namespace