You should definitely not be afraid to test your limits. By pushing yourself beyond what you normally would do is not a bad thing. For example just think of it along the lines of a rubber band. The rubber band is attached together.
Then after you keep stretching it, eventually it breaks. After the rubber band breaks you can stretch it even further. Your life is exactly the same way. Also your skills and everything else you do. Because you want to keep moving forward, learning new skills and sharpening your current skills.
Ways to go about testing your limits are to not be afraid of new situations. When you are in new situations do not run from them (well if its a life or death situation then run) and learn what you can from the experience. Because doing so will allow you to grow to the person you should be.
After you’ve experienced new situations is time to start doing what you know you should be doing. I know I probably have talked about this before. But I over time you will learn that it is so easy to just let things slip by. When you know that you should be updating your portfolio site more often or when you know you should be marketing your website more often. But instead you just keep letting it slip by.
Testing your limits is really for someone who knows that they are capable of doing more then just what is required. Also someone who wants to see how far they can go. By seeing how far someone can go they will eventually surpass others who just do what is required to get by.