It's being built to test the EmDrive, but it might be useful for testing the Mach Thruster too:


"The resolution lies in designing a tool that can measure these minuscule
amounts of thrust. So a team of physicists at Germany’s Technische Universität
Dresden set out to create a device that would fill this need. Led by physicist
Martin Tajmar, the SpaceDrive project aims to create an instrument so sensitive
and immune to interference that it would put an end to the debate once and for
all. In October, Tajmar and his team presented their second set of experimental
EmDrive measurements at the International Astronautical Congress, and their
results will be published in Acta Astronautica this August. Based on the results
of these experiments, Tajmar says a resolution to the EmDrive saga may only be a
few months away."

See:

https://www.wired.com/story/a-mythic...s-a-real-test/