Could you please elaborate more about your test scenario. Do you need to connect to the popup window and perform actions on it?
If that is the case, you can use code that is similar to this sample code against a public site with a popup child window:
//Turn on new browser tracking before the popup link is clicked
//You can now turn off new browser tracking
//Check whether the ActiveBrowser is now the popup.
Here is a short video
, which demonstrates it.
Hope this helps.