I have never done one of those test, but, common sense tells me that in order to see how a reservation system works they have to issue more fastpasses for that attraction. In fact, they have to issue, at least, the number that is the days capacity in order to see if it works. What it simply means is that Fastpasses will be available for those that otherwise would have been in stand-by. It is no more discriminatory then the stand-by line itself. When they reach the end of the day only those that are within the ride capacity will ride with or without a FP.
On the surface, yes, that is how it would appear. But - and this has been said on pretty much every thread regarding FP-only lines -
decreasing the wait time
increases demand. TSMM is consistently above a 60 minute wait most days of the year, and for some people, that is "too long." But that is their opinion based on the wants and needs of their particular vacation. To some people, the ride
is worth that 60+ minute wait, and they are willing to wait that amount of time. Whether it be because Toy Story is their favorite movie, they love the interactive aspect, or it's the only damn ride in the park their little one can ride - they want to ride it, maybe even a couple of times, wait time be damned! In a nutshell, the line is self-regulating. People will only enter the line if they think the value of their experience will exceed the wait time.
But wait, what's this?! Now no one will EVER be forced to wait more than 10 minutes (or whatever the amount) for this? Well, now everyone who had only mild to little interest in this ride thinks, "What the heck, I can get on without waiting, why NOT do it?" More people are willing because it costs less of their time (i.e. money). So now barely-interested Joe Schmoe could very well take the spot of the family who loves TSMM above all else. Yes, yes...if they loved it so much, they should have gotten a FP+, blah blah blah, but some of us are CMs who cannot book ANY FP+s in advance, and so I would love for someone to tell my children that they cannot ride their favorite ride in the entire world even if they're willing to wait two hours (mainly because it's the only way sometimes with FPs being gone so early) because someone else with deeper pockets whined that waiting in line was just too darn hard and inconvenient is now being given their near-immediate access at the expense of people who are
willing to wait (earn, if you will) for their spot on the attraction. And it doesn't have to be CMs or locals who will be negatively affected by this, I just use that as an example.
Basically, the less effort (waiting) involved to ride an attraction, the greater the appeal, the higher the demand, and the more likely even the most devout fan (or even you!) will be blocked out.