Today I share this holder I created. Had to print several in order to accomodate a donation of 29mm test tubes that my wife's school received.
Hope it fits your need. They look nice, they print with a small ammount of filament, and are designed thinking in stability and avoiding liquid drops to remain in its surfaces.
I printed them in PLA with 20% infill and no brim nor support.
In these few days exploring 3d printing, I found a perfect oportunity for improving my autocad skills and learn to consider in depth general design issues. My feeling is that 3d printing will improve the way humans develop things. We are experiencing just the begining!