I applied online and took around 3 weeks before I got an email from the HR for an initial interview. She asked me behavioral questions. I think it went well because they sent me a take home test. All the people seem to get the same test. I solved it and sent it back the same day. I was told they would get my test checked and reply within couple of weeks. No reply came, even after 3-4 follow ups over a period of a month.

Brief phone interview, hour remote technical interview, half day of (mostly technical) interviews at their office. It felt suspiciously easy. I would be wary of them using you for interview practice. That is the best explanation I can think of given that (1) they had a practice interviewer for an hour, and (2) their purported reason for not making an offer was that I did not have a specific technical skill, of which there was no mention until then. Other explanations are possible, but I would make sure to ask if there are any specific technical skills required. On the other hand, everyone I interviewed with seemed intelligent and nice. I think they would be enjoyable to work with. The experience was enjoyable, in a sense, but felt like a waste of time.