Their on-site interview was different than most other companies. I'd like to mention two rounds, one "Integration", one "Bug Squash", which both required you to download some code source from git repo and you would need a local environment setup to run. Integration round need you to understand HTTP Rest calls, parsing some Json and sending requests to some API server, I managed to get the code completed with some googling of new libs/apis. Bug Squash round need you to understand their code base and fix multiple bugs based on some test case failures.I was able to fix partial of those, what I could tell was that some bugs tend to be easy but some could be difficult, especially when code was compact, lack of comments, or it touched some advanced componments of a coding language which you probably never/rarely used. There's no much need to prepare hard for their interview and I didn't expect to pass interview from the beginning, just try your luck.