There are a few failure modes: physical break, corrosion/clogging, and electrical short.
For a physical break, just inspect closely for cracks. I don't think the DCCV has the micro-crack problem, so you're looking for more obvious issues, like a hole.
For corrosion, you can just momentarily connect the outer pins to v+ while the center pin is grounded. The solenoids should fire, with the plunger smoothly extending and retracting. Close inspection inside the water passages will also tell you plenty. The heads of the plungers should be clean, and the area they contact should be smooth.
For electrical, the specifications are in the service manual. It's a basic resistance test to ensure the coil windings and connections haven't broken.
In my case, the difficult to track problem was a driver in the DATC was partially failed and didn't sink enough current to fully actuate one of the solenoids. This took a little more investigation, but there are procedures in the service manual.