(nb: semi? thread hijacking......apologies again)
unfortunately the experiment does not "test against the speed of light"....the experiment was actually testing against the speed of light (?)
only objects that move relatively to the earth will show a result that is detectable using light motion as the tool....those that remain at rest (like the components of the interferometer) will not return a positive result.
this effect is detailed by the range of velocity values vs doppler shift that is obtained via the science of doppler radar.
doppler shift reduces as relative velocity (to the earth) reduces...until finally we have no doppler shift when the components are held completely at rest with respect to the earth.