Healthiness preservation

[QGarchery]

HEAVILY inspired from this gist, thanks @daejunpark !

[Rubilmax]

I think it can be refactored to inherit from existing invariant tests handlers (so we have less redundant code) by separating the current invariant tests into 2 layers: one with the handlers, one other with existing invariant tests. Yours should then inherit the handlers layer and it should save at least a few lines of code

Another thing: there already exists a src/mocks folder for hardhat and forge tests (required to be in src by hardhat)

[QGarchery]

I think it can be refactored to inherit from existing invariant tests handlers (so we have less redundant code) by separating the current invariant tests into 2 layers: one with the handlers, one other with existing invariant tests. Yours should then inherit the handlers layer and it should save at least a few lines of code

Another thing: there already exists a src/mocks folder for hardhat and forge tests (required to be in src by hardhat)

Yep, trying to do all of that but I am facing unexpected errors where the rate is not taken into account. I'll put it as ready for review when I have resolved those issues

[QGarchery]

Replaced by #598 because it's simpler and it gives an computation to ensure that your loan is safe for a period elapsed