Typically, the 25mph setup means that the trailer brakes actually stops the trailer tires from moving, causing them to skid and giving off the screech and squeal you might expect. The whole setup will lurch to a stop. You back down from there.
But, I have had a trailer that never squealed to that extent so "lock up" can vary depending on your trailer and the brakes. It also can depend on how new the trailer brakes are as I understand it and how warmed up they are for the test.
I look to obtain a noticeable braking action from the trailer while the whole setup stops simultaneously and smoothly. When I have completed the 25mph test successfully, the manual lever slows down the trailer and TV smoothly and reasonably quickly without jerking.
The goal is to get a smooth uniform stopping action with the trailer and truck brakes working in conjunction.
DW, 3 Kids and our Goldens
2012 Shamrock 233S
2008 Toyota Sequoia 5.7L 4WD