For example, if you have a developer doing something technical - how can you ensure it's done correctly?
I suppose you could have them do the work and then have a separate dev check the work (if resources allow)?
Interested in potential ideas - treat this more as a brainstorming activity where all responses don't need to be entirely practical.
Is there a reason you couldn't simply act as the user and test it out? Most QAs I have worked with have not been technical either.
Ask ChatGPT how it would go about making something with similar requirements, step by step, and then feed it back the source code you get from the dev and ask it if it's a reasonable way to approach that problem. It's probably going to do better than hiring another rando dev who you don't already know to be trustworthy. Tell it you're not technical and to explain what the code should do in a best practice situation and compare it with the source code you actually provided, explaining differences in layman's terms.
Another way would be to learn some technical details so you understand what they’re saying and doing instead of writing yourself off as non-technical.
A worse but doable way is to have someone with expertise check their work. That only makes sense if you don’t trust your developers which is a pretty bad situation.
Your question is weird because it’s sort of like asking “How do you know if a contractor is building a house properly when you don’t know anything about building houses?”
It usually helps if you look at the problem from a different perspective.
Any kind of testing should be defined at a high level. What is being tested and what is the expected result? What should trigger an alert?
Trust your people. If you spend all your energy trying to second-guess whether they are competent, they won't stick with you. And if they did not deserve that trust, it will show in their results quickly enough anyway.
Same as anybody else, just see if they can deliver on what they say.
More developers is better though, as you’ll be able to compare multiple perspectives, which can reveal dishonesty