Hook to run functions after invariant test run

[sveitser]

Describe the desired feature

Foundry allows defining a function afterInvariant that runs after invariant tests. It's briefly mentioned in the docs on this page.

We're using it to run print some stats, run some extra asserts that are slow to run and to withdraw all funds from a contract to ensure all users can withdraw what they own.

I couldn't find such functionality in echidna so currently I'm skipping it for our echidna test. Is it currently possible to do something along those lines? If not, is this a feature you could consider adding?

[sveitser]

I think one could achieve something similar enough by doing the final withdrawal in a fuzzed function (with some low probability) and then either end the test and or even continue the invariant test.

[gustavo-grieco]

It is unclear to me if Foundry runs afterInvariant after a sequence is executed or if runs after all the campaign finished. In any case, it is not possible to run a function that will run always in these conditions yet. Normally, in invariant development, you have functions that perform some asserts under some preconditions. If the preconditions are not met, the code just reverts and let the fuzzer find where it makes sense to call this function. I'm still open to discuss this feature, if we can find a number of good use cases.

[sveitser]

Thanks for your answer.

It's after each sequence. However, the case of logging is handled specially in foundry and only the logs of the last sequence are shown in the terminal (this was really unexpected/confusing to me). I used the extra logging to get a bit more visibility about which functions are called how many times.

My use cases are:

• Logging stats about function calls, mainly for debugging until I was convinced I covered what I wanted to cover.
• Logging info about the final state of the contract under test after the sequence is finished.
• Cleanup: in my case this ensuring that each participant can withdraw their funds.
• Checking invariants that are relatively slow compared to other steps.

This isn't super high priority for me but I was wondering if I just didn't know how to do this or if it's indeed currently not easily available.

[gustavo-grieco]

Personally, I want to implement proper setUp, beforeInvariats and afterInvariants, but we need to do an extensive refactoring of the Campaign.hs file before doing that. In general, I think we should take the good ideas from Foundry, and these are reasonable to have. What others do you think we could add as well?