I applied online around 3 months back. I received the online assessment over a week back containing a debugging section - 7 questions for 20 minutes and an analytical reasoning section containing 24 questions for 35 minutes. I had all test cases passing for the debugging section and finished that 10 minutes early. I was short on time in the Analytical Reasoning section. I am guessing the analytical reasoning section was the reason why they rejected me. If you write code on a daily basis and have a lot of project/internship experience, you probably don't need to prepare for the debugging questions. The best way to practice would be HackerRank/LeetCode. Also, make sure you read the question properly and analyze what's wrong in the test cases when you run the given code. That should give you a big hint about what to fix in the code. The bugs are usually very simple but also very common among programmers. For the analytical reasoning section, make sure you practice questions that you can find online. The questions individually are not that hard but you need to be fast in solving them.