Since I was already an intern, I went straight into the written test. The test is timed and fairly difficult depending on your knowledge base. I barely passed but still moved on and got an offer - so not sure how much they value it. My panel interview day was a 30 minute presentation following by 5 back-to-back 45 minute technical interviews. Difficulty really depended on your interviewer - some asked only technical questions and others had more of a conversation with you about design decisions relating to your project or projects at Tesla. Pretty much just know your fundamentals and how to work through a question even if you forget that specific topic. Then after you pass the panel, one shorter and more relaxed 30 minute technical interview with the senior manager