If your car is parked for winter, maybe you have the battery drained, disconnected or removed, or perhaps the door lock unit or some other component of the lock system is defect, you can still test your solenoids outside of the car. I removed mine with help of some good online instructions, to replace them with actuators. I still wanted to test the solenoids however, even if I am going to replace them (if your solenoids are ok and you replace the relays inside the Door Lock Control module, since the original ones tend to stick and thus shorting and damaging the solenoids, the system should last for many more years, but the solenoids are heavy and you will notice a significant difference in door lift with actuators instead.) Here are som resources i followed when removing my solenoids:

• An official video from DMC about how to access the doors
• How to replace the lock solenoids for actuators
• How to get inside the door and remove the window
• How to rewind your lock solenoids
• How the lock system works, the Door Lock Module and the solenoids

Now to the testing part. You need a 12v power source that can supply a fair amount of amps, I was recommended  at least 10 amps. I used a portable jump starter which is capable of supplying 500 amps, and it worked fine. The solenoids will only draw the amount of current they need. Just be sure to pulse them, like i do with the nail, not supply the power for a long time, because if any of the two coils inside each solenoid is shorted, they can get hot and further damaged. Note, you will most likely experience some heavy arcing when touching the contacts due to the many amps, but it is ok. Make sure you are on a protective surface and perhaps use safety glasses. Here is a video showing my testing, i learnt mine actually worked fine, except for one coil in one of the solenoids: