There is a system tag that holds a bit array of SystemFlags. The lowest order bit is on if you are in the designer and the next bit is on if you are testing in the designer. I usually use an expression like this in the visibility property of a component. It is visible in the designer when not testing but uses the other condition when testing or at runtime.
({[System]Client/System/SystemFlags} & 1 ) // in designer (bitwise and with lowest bit)
&& // and (logical and)
!({[System]Client/System/SystemFlags} & 2) // not testing (bitwise and with next to lowest bit)
|| // or (logical or)
{your/tag/that/controls/visiblity} // your condition(s) ...