Sorry for the misleading documentation. Windows and popups lie above main HTML content of the page and they don’t obey container property because a special container with high z-index is created for them anyway.
At the same time adjust() method for window adjusts it to the size of a parent HTML container of the view that lies inside window body.
So you can just set fixed dimensions for a window to match the size of a testA div.
I was thinking more in line of a built in alternative to using setPosition, config.width, config.height, resize() and getting the HTML container size by using getNode().