I'd ask for a detailed description of the types of work you will be doing, and seek your own self-assurance (whatever they tell you) that your development skills won't atrophy.
Moving from a QC/testing role to development can also be a hard sell. Don't get stuck/typecast.
I suspect that, the larger the organization, the more true a lot of this is. For one thing, QC/testing changes from being a few individual roles to its own entity, depending on the organizational structure.
If you can, spend some time networking with people in and about this kind of role. If you can make some safe connections to people at the potential employer, all the better. But also try to ascertain whether the move will have any negative career implications. (I'm just one introverted bloke, and my experience is likely biased.)