Test reverts with Assertion failed. when reverting to a fork snapshot, without any assertion

[Rubilmax]

Component

Forge

Have you ensured that all of these are up to date?

• Foundry
• Foundryup

What version of Foundry are you on?

forge 0.2.0 (15204ec 2022-11-29T00:07:45.954046141Z)

What command(s) is the bug in?

forge test

Operating System

Linux

Describe the bug

Report

• The following test case testWtf reverts with reason Assertion failed., whereas no assertion is explicitly performed within it

// SPDX-License-Identifier: GNU AGPLv3
pragma solidity ^0.8.0;

import "@forge-std/Test.sol";

contract Config {
    address public test = 0xcBa28b38103307Ec8dA98377ffF9816C164f9AFa;
}

contract TestSetup is Config, Test {
    function testWtf() public {
        uint256 snapshotId = vm.snapshot();

        vm.prank(test);

        vm.revertTo(snapshotId);
    }
}

• forge-std is at the latest commit: ea1c1f4022f6a7924887106caa64499317295493

Findings

It seems to be a very specific case, because the test passes as soon as:

• the order of inheritance is swapped
• the test address is moved to the TestSetup contract
• the test address is address(1), address(2), ...
• any of the line of the body of testWtf is commented out

The test fails even if a call is performed on behalf of the pranked address test, right after vm.prank

[MerlinEgalite]

Nice bug ser

[mds1]

@mattsse, potentially related to #3055 (comment) and foundry-rs/forge-std#241?

[mattsse]

thanks, will fix next.

[mds1]

@mattsse This still appears to be an issue—seems something is broken with the snapshot/revert functionality. Giving this high priority since it causes in erroneous test results which is bad 😅

[ZeroEkkusu]

Hi, @Evalir.

I've seen that you've been trying to solve this issue, so I wanted to clarify a few things, in case it helps you.

I haven't checked the codebase, but it seems that before reverting the state, the thirty first byte of the zeroth slot of the testing contract is checked for a non-zero value.

If that is really the case, I suggest you check the slot at the Keccak-256 hash of the word "failed" at the VM address first, to see if the value is one (and it will be).

That is because placing a contract with a state variable before DSTest in the inheritance chain causes the storage order to shift, meaning the _failed flag won't be the second state variable anymore, that is, its value won't be the byte being checked.