Often when I write an answer I write some code to go with it, ie "this method is written a little weird, you could simplify it as X, Y, Z,
example". This code is not necessarily always perfect code - it might exclude some error handling, or some edge cases, or just not be written perfectly correct.
I then sometimes get a comment from the OP saying something like "this doesn't work for case T", or "this doesn't compile because of missing semi-colon", or whatever.
In my mind, when I review the code although I may rewrite all of their code to something that is more readable, efficient, or whatever, I never intend for it to be perfectly functional or compilable, or whatever. Rather I generally intend for it to be a general guide as to improving some aspect of the code.
Should I make sure that all of my code works perfectly and solves all of their needs? Should I make an explicit note that my code isn't tested and may or may not work? Should I just ignore people who blindly copy-paste my review and are surprised when it doesn't work as expected?