> Agile doesn't have that, there is no functional equivelant of "the cake should be moist and rise evenly".

That's not true for the way I understand agile. The way I understand it, the testable outcome is whether the principles of the agile manifesto are satisfied

For example, is your highest priority to satisfy the customer through early and continuous delivery of valuable software? If not then you're not agile.

https://agilemanifesto.org/principles.html