I had my first odd thing happen on my 2007 E550 today.

I was headed to work, having gone perhaps 7 miles so far. While going about 25 mph on a very small incline, the vehicle did a quick "lurch" or sputter that lasted a second or so, then was normal again. A few seconds after that the check engine light came on.
It was almost as if the car turned itself off, then back on.
It is equipped with keyless go, and the key was in my pocket.
I drove the last 2 miles to work, opened the hood to check the engine
The only thing I know enough to check was the oil, and it was fine. Still the color of honey, as I had it serviced less than 500 miles prior.

Coincidentally, I was going for a MD Emissions test today. I figured they were going to fail me due to the Check Engine light, but the attendent never said a word. When I got back in the car to drive it out, the Check Engine light was now longer on.

I had restarted multiple time prior to going in for the test, and the light stayed on every time. Could the fact that the test center plugged their computer into the car be the reason the light went off?
Will the car's computer have stored codes?

I'm confused!