Black Box Puzzles is one of few websites that actually can help you become better tester.
I have heard about this project in the past, but I didn't use it until couple of days ago. Perhaps the link was outdated? Or I have found reference on my ebook reader, which doesn't have Internet access? Or there was disclaimer about puzzles being in Flash and I haven't even tried?
Black Box Puzzles are... well, puzzles. There are no instructions for them. You may use them however you like - it's entirely up to you. You can use them to see how it is to use application without specification and to improve your model-building - and model-refuting - skills. You can play, you can explore, you can learn, you can understand, you can test. They are fun little brain-teaser to kill some time and to provoke a thought about how you work.
All puzzles are deterministic. They will provide the same output for the same input. To the best of their author knowledge, they are bug-free. There are no tricky parts to trip you over. Author promises they do simple things, but there is no guarantee that your definition of "simple" overlaps with his.
It's not all roses, though.
- Out of 21 puzzles, 12 are in Flash. They won't work on mobile device or any modern browser. In fact, I am not yet sure how to run them at all.
- There are no instructions, no specification and no oracles. That means you can't be really sure if your work is done. If you can predict response of system to every action you take, is this due to high predictive power of your model, or is it because you are really bad at thinking about tests that might refute your model?
- That also means that if you can't figure out what is going on, you are screwed. There is no hint that you could take or solution that you could look up. You will learn that you don't know something, with no indication what that something might be or how to fill that gap.
- You can't read source code of puzzles. Of course reading inner workings of puzzle out of their code could be considered cheating, but comparing conclusions that you can reach using black-box approach and white-box approach could be useful exercise as well.
Takeaway: Go to this website and do some puzzles.