Interesting in that I've not seen something like this before. Personally I hate dev tests, but a lot of employers seem to like them, so I can see there potentially being demand.

My first thought is that the tests are too easy, I'm a Ruby dev with only fairly decent JavaScript knowledge, yet I was able to complete your hard, 10 minute, javascript test in one attempt.

My other concern is you'll need a LOT of tests, that expire quickly, to stop people posting solutions online.

Best of luck :)