What are the possible ways to test a deck?
There are different ways of testing that you can do, but none of them are as effective as playing real games against other people.

1) Play without an opponent. I usually play new decks over and over without an opponent to see how the basic idea works out. Just draw and play and see how many rounds it would take you to win on average. Do your combos work out as you had hoped for? Do you have too much or too little mana available? Adjust your deck until you are satisfied with the results.

2) Analyze the meta-game you are playing in. What are other players going to play against you? Try to identify the main threats in those decks and see if you can counter them. Are you fast enough so that they do not matter or can you establish enough control to break their combos? If you find a common deck that you are helpless against, try to find a solution.

3) Put up your desk for analysis online. There are many forums with experts from the MTG scene. Post your deck in the appropriate forum and hear what others think about your deck. They usually will have more experience and find weaknesses without having to play the deck. If you have more specific questions than "is my deck any good?", the MTG experts from this site here (Board and Card games on Stack Exchange) will also be able to help. I learned a lot already here.

These three steps can help you a lot already. In addition you can analyze the Mana Curve of your deck and identify problems there. But in the end, finding practice partners helps the most. I have played MTG-games over webcam in the past with friends of mine. It works better than it sounds like in the first place ;). So even if you don't have anyone in reach, you can try to play with friends who live farther away over the Internet.