Gunrunnerjohn showed a two level support to test engines with connected tenders. It was a surface mount that can be used with one size of rollers. Since rollers for stationary engine testing come in various height, a one height two level support doesn't fit all.
Also, I have no space on my work table for a long extended test track. So my test track is elevated above my work table. The track goes from my workroom to the layout around the workroom, thru a wall, down the hall, across a cedar closet my wife uses ( so there is a lift bridge across the closet doors that must remain UP) then thru another wall exiting into the layout on a series of bridge supports into a spur that connects to the upper layout. Whew!!
So I cut a slot into the end of the test track, used the cutout as a track support, made two support lift stations that can be raised and lowered to accommodate the various rollers and of course return the track in the slot to the level position.
The lift station is a simple u-shaped support, inside it is a