Seriously, a lot depends on where you are (different countries have laws about what questions can't be asked), what kind of development process your team uses, your company culture, and the kind of applications your company produces. This isn't an exhaustive list, either.
That said, if there are developers in the interview, you would probably want to stay out of the technical side altogether, and focus your questions on how the developer interacts with QA, and how they handle themselves in general. Some thoughts on this line:
- What do you see as the ideal relationship between QA and development?
- Consider a situation where you had a conflict with a team member. How did you respond? How was the situation resolved?
- What have you taught yourself? How did that work out/help you?
Regardless, you'll want to let the candidate talk as much as possible and take not of what they don't say, and how they say things as much as what they do say. Also take note of their body language: an interview is a high-stress situation, but whether someone's posture is relaxed or confident or timid will tell you a lot, especially if that changes during the interview.
The object of the interview is to find out how the person thinks. Does their thinking align with the way things work in your company? A great question to start the conversation is: " Tell me about the biggest glory bug you found."
Let the interviewee define "biggest". It can be the most complex, most costly, gained the most news coverage, toughest to reproduce, whatever. The interviewee will recount the story. Be sure to find out how the person found the bug, what was done to advocate for its fix, what sort of initiative the person took above and beyond the call of duty to set things right. What did they do to fix things right now, and to ensure it and things like it never happen again? What did they learn from the experience?
This single question and the natural follow-up questions will tell you about how the person reacts to a situation that requires advocacy, leadership, collaboration, tact, business sense, and technical skill.
- Do you use Behavior Driven Development ?
- Do you use Test Driven Development ?
- How do you do sad path testing ?
- How do you structure test plans ?
- How do you approach the 4 quadrants of Agile Testing ?
- Do you use the Test Pyramid ?
- What do you try to capture for a typical UI bug ?
- What sort of relationship do you look to have with the QA group ?
- How do you try and address intermittent failures in the test suite ?
- What experience do you have with performance testing ?
- What's the most interesting bug you've seen at work ?
- Do you have one assertion per test and do you make exceptions ?
- What is your experience with team-based vs. more role based development ?
I would leave the more detailed coding questions to the dev team.
Focus on your area of quality and testing