You don't have to (and should not) request access to the whole codebase, simply asking to see a single medium sized file from a project you would be expected to

You don't have to (and should not) request access to the whole codebase, simply asking to see a single medium sized file from a project you would be expected to work with is often enough. I've asked for this before with great success, some companies will ask you to sign a short NDA beforehand, most don't even bother. Sure, it leaves the chance that they will simply show you the pretty parts, but at least you'll know that there are some pretty parts at the very least.