I have open source code (about 13k lines of c/c++ for embedded platform) and I happen to interview 'badly' when I am put on the spot and asked to code up something in 15 minutes while someone watches me. that's not how I work and I fail horribly at THAT style of interview. note, I am fairly good (not a+ but definitely better than average) at coding in the real world - just NOT in synthetic white-board style interviews.
As a designer, this type of thing floors me. Every job I've gotten (and every job any designer has gotten) is based on their portfolio. Nobody asks if the person actually did it, or was helped, etc. They ask you to discuss what you did. That's been the standard for getting design jobs for decades.
I don't understand why developers don't have portfolio reviews like this as well. What they're asking of you is akin to someone asking me in an interview "draw us some pretty pictures". Most designers would find that an offensive disregard for the practice of design, let alone a disregard for the previous work they've done that should be the actual litmus test for getting the job.
Developers need to start putting their foot down and asking for portfolio reviews of code they've written and not be asked to do a side show act to get jobs.