While it may be possible to tell competance easily this way, one thing I found difficult to tell without live coding is someone's ability for architecting compo

While it may be possible to tell competance easily this way, one thing I found difficult to tell without live coding is someone's ability for architecting components. One recent hire at work is competant at coding, but for a senior engineer, weak on designing API for a UI service to generate components, as well as weak on unit testing (which in this instance, turns out to be somewhat linked). How would you screen such a person out?