That depends heavily on what they're actually screening for. I've received an embarrassing number of utterly atrocious code challenges from candidates in the past. If you can't code something like a roman numeral generator/reader (when allowed to do so at home, in whatever language you want, spending as long as you want on it) then continuing the interview process at this point is a huge waste of time.

In those processes, the purpose was to weed out people that simply could not code at all. Or even cheat, since there are solutions all over the internet for any language you want.

A later stage was to do some programming with us, and we'd talk through issues and see how they dealt with problems/etc.