Overcoming any addiction is achieved my taking small steps to reduce your habit until you are comfortable to keep it at a bare minimum or avoid it completely. In case of some activity like playing video games etc. you can start by reducing the time you put daily into it by 5-10 mins every day/every other day.

Well, but I'm not addicted to gaming. I'm addicted to taking typing tests like I said. Luckily, I spend just 15 minutes taking them every day and I feel uncomfortable when I don't.

Then you're not addicted to typing tests

Nice joke :D :D

If you like typing that much, and you have RSI, I would recommend learning a more ergonomic keyboard layout like Colemak or Dvorak. Seems like a perfect fit for you.

Maybe you could embrace your hobby and get an Ergo dox or something similar. It'll help out with your RSI issues, and give you something to strive for - new speeds on an unfamiliar-ish layout. I think it's a great opportunity to put yourself first and at the same time get a new challenge to overcome.

That's just my two-sense, though. Oh, and keep in mind, the Ergo dox is pretty expensive. Just FYI.

I own a ergodox and personally I don't like it. I would say something like the iris keyboard is better.

If I was the op I would go all out and build a manuform.

I guess I would suggest letting out the tension in your fingers or hands after each typing session like soaking it in warm or hot water or a warm towel and try out some good typing habits that reduce strain; i.e. palm rests, etc. I type on the daily too for about a year now and I don't have any strain injury since usually just crack my fingers and stretch them if I feel the need to but I guess that's not for everyone to be able to do to reduce strain and might even cause injury if the person doesn't do it even before they learned typing.