Even then I'm not sure it would have saved me from the worse code base I ever worked with, the only one I flat out decided had to be replaced (after spending a month fixing some bugs and learning it took days to determine how to safely fix one, the code was so tangled).
In reference to the NDA comments, if a company is too paranoid about that sort of thing without clearly having "special sauce" worth protecting---unfortunately, future products or product directions can also both be worth protecting and necessary to disclose to you---that's a strong sign to avoid them.
And while I don't have a good way to express it yet, if they demur you can point out the above, and that quite to the contrary of whatever they're worrying about, they'll have to pay you good money to seriously examine their code (and then work on it) ^_^.
Asking to see their code is obviously a bit different than being offered to use it in some interview coding demonstration.
The only time I ever interviewed with a company that wanted me to sign an NDA first they faxed or emailed me a copy at least a day ahead of the interview.
In one case where they told me about it ahead of time, I refused to accept it, and they refused to interview me.
In one case, facing this last-minute NDA, I wrote on it just above my signatures something like "it is understood that nothing confidential and proprietary will be shared with me and so this agreement is effectively void". The receptionist had no issues with it (she didn't even read).
In another case, the NDA was offered on an electronic display with a signature pad (so I could not make any edits). I decided to proceed in that specific case.
These same agreements often say that you'll not disclose anything confidential and proprietary to them. Yet they openly ask those questions. Some often even expect your previous code samples should be publicly available on Github. (I am looking for a chance to ask them if their IP contract allows employees to put their code on Github.)
The root-cause of this problem: It is not the companies or the lawyers, it is the most of us who sign these agreements without reading. The latter tilts the equilibrium for the contracts in the favor of the companies.
WTF did I just sign?
The real danger probably isn't that they'll try to enforce it per se, but that they could make you "radioactive" by the threat of it, or an enforcement action, even if ultimately unsuccessful. Hopefully no or few potential future employees will ask about them, and if this happened in California and you're still they (it gets more complicated if you're only now in the state), any non-compete provisions are unenforceable as such.