If you are trying to user test a physical product (or anything for that matter) make sure to first and foremost give the user tasks to undergo.
For instance, if you are trying to get a user to test a new hard line office phone you would want to create tasks such as:
- Go to your directory and call John Doe
- You just received a call from a co-worker, and you don't have the number, how do you redial?
Make sure the tasks are simple and straight forward, but are exactly for what you want to achieve. For instance, the above tasks would provide answers whether or not your interface is clear and concise. Also it could provide some insight on how users handle the phone.
Here is a good resource to use for user testing and other matters concerning usability and the like: http://www.nngroup.com/topic/user-testing/
Further more, you need to be specific with your question so we can give you a specific answer. Instead of asking us about user testing methods for physical objects or items, you should say for example: "user testing methods for a mobile phone." This allows us to give you better feed back since I can tell you weren't satisfied with my or anyone else's answer. Help us help you! :)
A quick breakdown of how to do simple user testing no matter what your product is:
- Before hand, make sure to compile a list of tasks.
- Make sure to then find people who fit in your user base
- Make sure to vividly record (whether by camera, notes, screen capturing, etc. I prefer videos, it helps way more and miss way less... Actually you miss nothing)
- Remind the user before hand that this is not testing them, it is testing the application or product.
These are incredibly simple however, I suggest you also take a look at these articles because they deliver vivid points on what to do and how to make the whole testing process way more efficient. This way of testing works for all forms of testing, just adapt to your needs: http://www.nngroup.com/articles/authentic-behavior-in-user-testing/
Everything else you can find are on the site. This site is phenomenal. Best of luck!