I was contacted by an agent and forwarded a take home exercise, and I have completed it in TDD approach, I was very confident about it. After 5 days she said she received feed back from CMC and told me that sanity checks fail. Really doubtful how those sanity checks fail when there are tests already to guarantee the requirements are covered. And the worst thing is you will never know about the other party at CMC you are dealing with, so you have to be ready for such simple feedback.