Proper Trailer Brake Function Check???

The trailer is not supposed to stop the truck. All you want to do is not let the trailer pass the truck on a fast stop.

I check my brakes in conjunction with my pull test function check of the hitching after backing onto the hitch. I do not rely on a visual check or the sound to determine if I am safely attached, though I do listen for the sound and look it over after the jaw trips. I lift the front jacks a few inches off the ground (hydraulic in my case, so one is all the way up and the other is a little bit elevated), keep the chocks in place, then manually apply the brakes with the brake controller while applying a very small amount of accelerator in forward to pull gently against the hitch and chock. If I am hitched and the brakes are working, I should feel the resistance. If I am not hitched properly, the hitch will disconnect and the trailer will drop at most 1 - 2" if I don't stop before the king pin comes free. Better than dropping on the bed rails. It has never happened, but I still do this every time I hitch. Since I have a factory installed brake controller, I also see the controller output on a display in my dash, so I have a secondary wiring continuity check as well.

I'll point out that this will not replace the need to periodically check the brake pads, etc. It is only a check of the braking system function, primarily the wiring and controller.

I have on occasion applied the brakes manually with the controller at low speed when I had some reason to doubt everything was right, but I do not do this routinely. You have to be on the right road, speed and traffic conditions to do this type of check.

My first question. Can be brake controller be set up high enough to lock the trailer brakes?

What controller are you using and what is your setting?

Brake Pads and especially brake shoes will need to be broken in per axle makers specs. After the break in period then is the time to test a trailers braking system and make adjustments/changes to suit you.
All my service and rv trailers brakes will slide the tires with high brake controller gain after I do my R&R and amp checks on them.......after their broke in properly.

I set mine so stopping with the trailer feels very similar to stopping without a trailer when applying the brake pedal. When the brakes are set right and I slide the manual control I feel the trailer brakes pulling very aggressively. The proper setting for my truck/trailer is 5.

Before I pull out of the driveway, I apply the manual brake lever and when the truck doesn't move, I know the system is working. My driveway goes downhill and at idle the truck will move on its own. When in a level spot I apply some fuel peddle to get the truck to move.

I pull my wheels and check brakes for any grease on the pads each Spring, replace the seals and hand pack bearings. There have been no bad experience with drum brakes for me so far. To test the brakes I just roll along at about 25 and pull the hand actuator. If I feel the brakes come into play I assume everything is ok. When I'm driving on the Interstate or any roads where my speed is constantly beyond about 55 then I use the top setting on my controller. If I'm in heavy traffic I use less setting.

After you pull for a while you will get a feel for your brakes. You can tell if they are working like they should. I don't believe a timed duration on stopping tells you much other than you know they are working properly. I like changing my brake controller setting for different conditions. Just my opinion and style I suppose.

I don't know of a timed procedure for testing brakes. I always accelerate to about 25 and hit the manual slider without using the vehicle pedal. If I feel resistance and it slows my progress, I feel it's good (per the users manual). My average setting is 6. I do switch settings between my 32' and my 28' due to the weight difference. This has worked for me for 16 years. As far as working poorly when you first pull out, I would ask how long does the coach sit before trips? Could be a thin layer of rust on the surface of the drums that will grind off after repeated stops. Same if you have rotors.