Try looking at Stack Overflow questions in a particular subject area. If you can answer 80% you're probably on top of it. If you can answer <20% you're probably

Try looking at Stack Overflow questions in a particular subject area. If you can answer 80% you're probably on top of it. If you can answer <20% you're probably a long way from mastering that subject and need to practice more. Many of those questions probe really odd behaviours you'll rarely see, so they're great training. 95% of what you do as a developer uses maybe 1-2% of your actual knowledge. It's the remaining 5%, those ugly bugs, those quirky edge cases, that really test you. The more you can expose yourself to those outliers, the more quickly you can gauge your knowledge. It helps assess if you're really good at just going through the motions, or if you actually have a deep understanding.