Your example code should work and be error-free
This is one of those cases where I'm undoubtedly preaching to the choir, but one thing that sends me into a moderate rage is articles about programming that helpfully include sample code as illustrations but then have errors in the sample code. The worst errors are subtle errors, things where the code almost works but occasionally is going to blow up.
Actually, let me clarify that. It's common to omit error checking in sample code and sometimes the demands of space and comprehension mean that you can't really put in all of the code to handle the full complexity of a situation with all of its corner cases. But if you do this you should also add a note about it, especially about unhandled corner cases. Omitting error checks (especially without a note) is more forgivable in a language with exceptions, since the code will at least malfunction obviously.
Perhaps it is not obvious to my readers why this is a bad idea. The answer is simple: sooner or later someone is going to either copy your sample code into their program more or less as is or use it as a guideline to write their own. After all, you've already given them the algorithm and the structure of what they want to do; why shouldn't they copy your literal code rather than rewrite from scratch based on their understanding of your article? If your code is good, it's actually less error-prone to just copy it. Of course the exact people who need your article and are going to copy your code are the people who are the worst equipped to spot the errors and omitted corner cases lurking in it.
The more subtle problem is that anyone who does know enough to spot errors in your sample code is going to immediately distrust your entire article. If you have buggy code in your examples, what else have you screwed up? Everything you're saying is suspect, especially if the flaw is relatively fundamental, like a concurrency race, as opposed to a a relatively simple mistake.
(Since I've put code examples into entries on Wandering Thoughts, this is of course kind of throwing stones in what may well be a glass house. I know I've had my share of errors that commentors have pointed out, although I do try to run everything I put in an entry in the exact form it appears here.)
(This entry is sadly brought to you by my irritation with this article on some Go concurrency patterns. It contains potentially interesting stuff but also code with obvious, classic, and un-commented-on concurrency races, so I can't trust it at all. (Well, hopefully the concurrency races are as obvious as I think they are.))