Please do not use an existing networking framework (e.g., Twisted or asyncore for Python, ACE for C++, etc.) to implement the server.
...would be a massively positive signal to me as a candidate. Places that truly value "full stack" abilities like this seem to be hard to track down.
If I want to see code, I'll tell them beforehand that I want to build a little project together with them (less than 50 LOC) that does this one trivial thing, and that they can write beforehand if they want to. Then when they come in, we either build it together if they haven't done it beforehand, or we change the specs if they did. And no, no bonus points for doing it beforehand. That's just so that they can feel more comfortable in the codebase if they feel it's necessary (being nervous in the interview and all). I'm most likely not going to compare their code to others; I'm only interested in whether their code meets the company standards.
I've also fired many people. It's not hard to do, nor does it cost much.
So many of these recruitment processes are predicated on the principle of "what if someone lies to us?" for fear of hiring the dud. But in reality, it's so hard to bullshit someone knowledgeable that the actual risks are tiny.
Yes, I've encountered people who couldn't code. I've had such resumes passed to me by people (usually non-technical, or recruiters) telling me how awesome this person is (because they don't know enough about the subject matter to tell the difference). But it takes very little conversation about any topic one is knowledgeable in to sniff out someone's bullshit.
Think of it this way: You have a leak in your house and hire a plumber. The guy comes and tells you that you need this and that. How do you know he's telling the truth? Now imagine that you're a plumber who's been asked by a friend to sit in on the conversation. How long do you think it would take before you can confidently call bullshit on what he's saying?
If YOU know your shit, you can tell when other people don't. And if you DON'T know your shit, you're going to have a hard time no matter how much code they throw at you.
I'm in Europe, so it's not easy to fire wrong hires after trial period, but I have never even seen anyone admit that they made a wrong hiring decision.
As an interesting case, one company I worked at hired an architect who had failed their rather trivial coding test but interviewed well. That person, together with company management, ended up driving away several competent engineers.
I won't work any more for employers who don't require a programming test. Your experience may be different.
On Wall Street everybody uses coding puzzles to screen candidates. There is really no other way.
But the online coding-puzzle sites they use are mostly really terrible.
It has also been my experience (20+ years) that sociopaths and egotists (the ones who will try to bullshit you beyond a few ham-fisted attempts) are in such a minority that they're not worth basing your interview process around.
The only cases of hiring engineers who couldn't code that I've ever heard of directly from colleagues over my entire career (that weren't third-hand re-tellings) have been where he either was not interviewed at all, was only interviewed by someone non-technical, or was hired by someone non-technical over the objections of someone technical.
TBH I think this is a manufactured problem.
"When implementing the server, aim for scalability and robustness. (Many submissions fail due to lack of robustness!) Your submission should include a description of the steps you took towards those two goals. Keep in mind that the client may be buggy, or even malicious. For example, if a client connects to the server and sends an infinite stream of the byte 'X' with no line break, the server should deal with this case gracefully. Please do not use an existing networking framework (e.g., Twisted or asyncore for Python, ACE for C++, etc.) to implement the server."
Not only no, but fuck no. I settled for a job in the IT section at a bank working with COBOL and EJBs because of this shit, until I'd finally had enough, co-founded a company, moved to San Francisco and implemented a SANE hiring process that treated candidates like professionals. Most of us did, so I guess in a way these horrible and misguided hiring practices were partly responsible for the next resurgence, because we'd finally had enough.