I have seen the testing machines, but do not know how to make them. The idea would be to put the pylon "pipe" into a clamp and then have it push down on heel and forefoot forces, rolling from heel to toe, the repeat. These are very robust machines and what I've seen have been made by the companies that make the feet. I believe there is also an international standard that has to be met. Most foot manufacturers not only sell their feet here in the US, but also internationally, which have certain standards. I am familiar with the College Park foot, the Truestep. This was started by an inventor who saw the movie Terminator and decided to create a foot for people to use with that design. He had gone through many different designs, using stainless steel, composites and a large varied about of materials. Since 1986 they have been making feet for amputees.
Here is the website for College Park, in fact there is a picture of one of the testing machines on the site.https://www.college-park.com/about/company