The basic control skills & road test portion of the CDL skills test exam will demonstrate your ability to operate a commercial vehicle in real-world driving scenarios.
The testing will take place on a state-approved route in the general area of the testing facility, and will include all of the things that you would normally expect to encounter when driving: turns, intersections, curves, city and rural driving, merging, etc.
Article - Passing The CDL Road Test: What Are CDL Examiners Looking For?
There are several things which may be considered an automatic failure on a road test. Some are obvious like don't get in a wreck or run a red light. But some aren't so obvious. Smaller things like hitting a curb, forgetting your turn signal, rolling backward before taking off from a stop, or not checking your mirrors properly before changing lanes.
Commercial Drivers License Manual: Section 2.15, Railroad-Highway Crossings
Railroad-highway grade crossings are a special kind of intersection where the roadway crosses train tracks. These crossings are always dangerous. Every such crossing must be approached with the expectation that a train is coming.
Article - CDL Test Day - What It Was Like Taking (and passing!) the CDL Test
I was the first person to show up and was extremely nervous. I felt ready, but being tested is not fun! There are a million ways to fail, and only a hand full of ways to pass. All of the ways to fail kept going through my mind.
CDL Skills Test sample score sheet
Grounds for immediate failure: Causes or contributes to an accident, refuses to perform any maneuver, commits a dangerous act, cannot operate vehicle.
Forum - Failed my CDL road test. Stalled! :(
First of all, it's nearly impossible to stall a truck if you start in a low enough gear. In fact, if you start in first gear you'd have to just about stand on the brakes to get it to stall because there is so much torque in those engines.