I recently contacted by a recruiter from Amazon London for SDE2 role in its Alexa team.
For online assessment, the platform was AMCAT which has no capability to run your custom testcase for a problem, You can run the program which will run on all the testcases for that problem. You can choose any language of your choice.

It was a 90 mins test with 1 medium and 1 hard level leetcode problem. It had separate 15 mins to write approach and complexity for both problems. I don't want to share the exact questions because of Amazon's interview terms and conditions. First question was on string occurances in text and second question was on grid (can be derived as graph traversal). I finished both problems in around 70 mins with all testcases passing. Then I also added comments in my code.

After one day, I got a mail to schedule my online interview (phone screen).