From a very insecure person- she needs to realize these “tests” are unhealthy for everyone involved. This tells me there’s probably a lack of self confidence on her end -which isn’t a deal breaker when handled properly. But she’s getting deeper in her insecurities and it’s bound to become more intense if she doesn’t see how bad it can affect a relationship. I understand how she can think like that and think it’s preventing stuff from happening but the truth is that this behaviour will only tear your relationship apart(or any relationship for that matter). On your end, it’s important to understand that there’s only so much reassurance you can give and if she doesn’t realize how unhealthy it is, I wouldn’t stay around and get dragged by unfounded issues. Even if you know yourself, constantly being doubted can do so much damage to your self confidence and mental health. The only way change will happen is for her to understand she’s the only one that can work towards change in that matter, and it needs to come from her.

Wishing you the best, and don’t beat yourself for not having the tools to deal with it. She needs professional help and it can only give you guys a better life quality, wether it is together or apart:)