What should I test, and how, before calling for inspection? I have a standard digital multimeter.

For background, l
- ran four #6 conductors (red black green white) in 1'' conduit from main panel area (conductors not yet fed into main panel) to a subpanel in the garage, neutral unbonded.
- drove two grounding rods w/ continuous #6 bare copper conductor in (currently open) trench 8'' deep to ground bar, conductor in conduit where it exits ground and enters garage, stapled to garage walls, enters subpanel through a cable clamp.
- ran four 20A 120v circuits using three #12 conductors (red or black, plus white and green) in 1/2'' conduit, one circuit per conduit run, no shared neutrals, as thus: (1) switched to four overhead receptacles, first one GFCI, to plug in lights, (2) to single overhead receptacle, GFCI, to plug in garage door opener, (3) to four receptacles on north wall at 54'' high, first one GFCI, for general use (4) to seven receptacles on south and west walls at 54'' high, first one GFCI and is on the ceiling for pull point and future drop cord (I decided resetting that one won't be a pain, there's always a stepstool in the garage), for general use and tools.
- ran one 20A 240v circuit using three #12 conductors (red black green) to overhead receptacle (for pull point and future drop cord) and south wall receptacle (for table saw), no GFCI. I also pulled a un-used #12 white neutral in this run (for possible future 120v/240v use, neutral is connected to the neutral bar in subpanel and capped off w/ wire nuts in the boxes.
- conduit and boxes are all sched 40 plastic, glued together, conduit held to finished walls with clips every couple feet.
- conductors are THHN/TWHN solid wires.
- conduit enters subpanel with couplers, nuts, and the whatchamacallits that cover the ends of the conduit.

Hank

I've read that real electricians test every aspect of their work, and I'd like if possible to do things the ''right'' way.

This project is largely a learning experience for me. I'm trying to learn how to do things correctly.

Interestingly, he also said he'd okay me upgrading my main panel if I moved the laundry sink (that is next to amd below it . . . ). An electrician had earlier told me that location was unworkable. So, I may be asking about replacing a main panel someday - not sure I am up for that, I am okay with everything but I don't know how to shut off the electrical service to the house.

You should call the POCO since the protocol is different in different locations.

We turn off the main and pull ourselves, but then we also routinely install a new meter base and then jumper it to the old and put the meter back in the old base (main off) so power is only out for a short time.
After a final inspection by the AHJ the POCO is responsible for any upgrades to the feed and service conductors to the top of the meter base, and sealing the meter in the new base.

Some places go so far AS to drop the feed on the pole and then reconnect.