I've discovered a property that I think I can use to verify if a column has its filter applied. There's a control called a FilteringDropDown (shown in my original attachment of the DOM explorer), which derives from Control. It has a property called FunnelFillVisibility. When filtered, this property is Visible, otherwise Collapsed. It is fairly straightforward from here to add a verification step based on this property from the elements menu.
Thanks for your help!