Very good! I guess I have a bit more to add.... on regulating the test effort.
I would categorize snatch tests as such:
1) Max reps in given time (for example, the TSC - max reps in 5 minutes with specified weight)
1a) A person who can not do 100 in 5 min /200 in 10 min
1b) A person who can do more than 100 in 5 min / more than 200 in 10 min
2) Specified reps in given time or less (for example, the SFG snatch test - 100 reps in 5 min or less)
2a) A person who can not do required reps within time
2b) A person who can do required reps in time with a 20 sec or less to spare
2c) A person who can easily do required reps within time
So the focus might be:
1a) This person likely can't hold the bell for 5 minutes straight and is forced to take breaks, setting the bell down during the effort. Waiter's walks, slow-get-ups, or sets of snatches with 6-sec or 10-sec pause in lockout (idea from
@Steve Freides in a past thread) will help with this, and may be one path to improvement. Beyond that, see 2a) below.
1b) This person can snatch well but will be looking for technique tweaks like actively throwing the bell down into the hinge, and other tricks to improve the cadence while hitting the technique standards for each rep. They also might do better by holding back a bit (pacing themselves) in the first 80% of the time, then sprinting to the end. Credit to
@aciampa for this idea... it worked well for me in the last TSC, where I got 133 reps w/ 16kg in 5 min.
2a) Strength, skill, technique, hinge power, grip endurance, and cardio... all needed. Swings will help a lot -- no need to get all this from snatches. Mainly, just keep training -- but intelligently, not by killing yourself with effort and tearing your hands up.
2b) This person has the required strength and endurance but it's a really hard effort to get it done. The most important thing is getting an idea where your redline is. As with 1b) above, it's best to not push as hard as possible - but just a bit less than that - until the final minute. Again, just keep training, it gets easier.
2c) Good to go; just want to make it as easy as possible for quick recovery.
I usually try to get an idea what my average "best" pace is (for the given weight and for my current fitness -- it varies), then start out at that pace for a minute or so, slow down very slightly for the next few minutes, then speed up at the end. Also best if I can not set the bell down, and if I can hold the bell for 10 or more continuous snatches before a swing switch. (I might do better without a swing switch, but I prefer switching this way rather than hand-to-hand in the middle of a snatch). If I go too hard and am forced to set the bell down and rest, the result is not optimal and I usually feel like crap later.
I should also add, with most Hardstyle applications there is no requirement to hold the bell the whole time. Lots of people do set it down and take breaks. Some even do better with a sprint style -- sprint 10 reps, rest, sprint another 10 rest... sort of like the S&S "test" for 100 swings in 5 minutes. I just have a personal preference for the continuous effort if possible with snatches, and I feel like it works best for me in training and in testing.
) still being HS? Yes; 1) finding a bit of relaxation in the lockout rather than maximum tension; let the bell rest on the shoulder structure rather than all muscle holding it... keep the legs tight but not max-tight; 2) find the most vertical path of the bell both up and down; 3) use as much hip power as possible so you don't rely on the arm/shoulder for anything other than guiding the bell to lockout; 4) get the timing right in the hinge; 5) use your breathing to help you. 
