- Is it really a startup? If it is HR may be a small department or even non existent, just a secondary job for a regular staff member.
- What have they asked? Is it a set of a few unrelated or elementary code structures? This test is just separating the wheat candidate from the chaff otherwise.
- Consider that devs get fed up of waiting for HR due to the delays, and if it's an engineering manager they may have just bypassed that shit because actual work needs doing (I've seen this sooooo many times).
- How much are they paying Vs risk of being a scam, are you cutting your nose off to spite your face? If the salary is considerably better than what you expect, I'd do it, you don't get anywhere without a little risk.
- Did they ask you to sign an NDA? If they didn't, and you're still concerned you could test the waters here and ask whether you need to, company IP should be protected, so a manager should let you know if it is, and if it isn't, i.e. it's a test, you _should_ be good.
- 8-10 hours is excessive. 2-4 is the norm for these kind of tests, so directly ask them for something more practical. That amount of time IS fishy.
HR usually agree with the engineering manager a budget, and the manager tells HR which candidate they want to hire. HR only is responsible for background checks in my experience.