01function invariant_totalSupplyMatchesBalances() public view {02    uint256 sum;03    for (uint256 i = 0; i < actors.length; i++) {04        sum += token.balanceOf(actors[i]);05    }06    assertEq(sum, token.totalSupply());07}

01import {Test} from "forge-std/Test.sol";0203contract StablecoinTest is Test {04    MockStablecoin token;0506    function setUp() public {07        token = new MockStablecoin();08    }0910    // Fuzz test — 단일 호출의 인풋 변화만 본다11    function testFuzz_TransferRespectsBalance(address from, address to, uint256 amount) public {12        vm.assume(from != address(0) && to != address(0) && from != to);13        amount = bound(amount, 1, 1e30);1415        deal(address(token), from, amount);16        vm.prank(from);17        token.transfer(to, amount);1819        assertEq(token.balanceOf(from), 0);20        assertEq(token.balanceOf(to), amount);21    }22}

01contract StablecoinHandler {02    InvariantVm internal constant vm =03        InvariantVm(address(uint160(uint256(keccak256("hevm cheat code")))));0405    MockStablecoin public token;06    address[] internal actors;07    mapping(address actor => uint256 balanceAtFreeze) public frozenFloor;0809    constructor() {10        token = new MockStablecoin("Invariant USD", "iUSD", 6, address(this));1112        actors.push(address(0xA11CE));13        actors.push(address(0xB0B));14        actors.push(address(0xCAFE));15        actors.push(address(0xD00D));1617        for (uint256 i = 0; i < actors.length; i++) {18            token.mint(actors[i], 1_000e6);19        }20    }2122    function actorCount() external view returns (uint256) {23        return actors.length;24    }2526    function actorAt(uint256 index) external view returns (address) {27        return actors[index];28    }2930    function mint(uint256 actorSeed, uint256 amountSeed) external {31        address to = _actor(actorSeed);32        if (token.paused() || token.isFrozen(to)) return;3334        uint256 amount = (amountSeed % 100e6) + 1;35        token.mint(to, amount);36    }3738    function burn(uint256 actorSeed, uint256 amountSeed) external {39        address from = _actor(actorSeed);40        if (token.paused() || token.isFrozen(from)) return;4142        uint256 balance = token.balanceOf(from);43        if (balance == 0) return;4445        uint256 amount = (amountSeed % balance) + 1;46        token.burn(from, amount);47    }4849    function transfer(uint256 fromSeed, uint256 toSeed, uint256 amountSeed) external {50        address from = _actor(fromSeed);51        address to = _actor(toSeed);52        if (token.paused() || token.isFrozen(from) || token.isFrozen(to)) return;5354        uint256 balance = token.balanceOf(from);55        if (balance == 0) return;5657        uint256 amount = amountSeed % (balance + 1);58        vm.prank(from);59        token.transfer(to, amount);60    }6162    function freeze(uint256 actorSeed) external {63        address actor = _actor(actorSeed);64        token.setFrozen(actor, true);65        frozenFloor[actor] = token.balanceOf(actor);66    }6768    function unfreeze(uint256 actorSeed) external {69        address actor = _actor(actorSeed);70        token.setFrozen(actor, false);71        frozenFloor[actor] = 0;72    }7374    function setPaused(bool shouldPause) external {75        if (shouldPause && !token.paused()) {76            token.pause();77        } else if (!shouldPause && token.paused()) {78            token.unpause();79        }80    }8182    function _actor(uint256 seed) internal view returns (address) {83        return actors[seed % actors.length];84    }85}

01# foundry.toml02[profile.default]03src   = "src"04test  = "test"05optimizer = true0607[profile.default.fuzz]08runs       = 25609max_test_rejects = 655361011[profile.default.invariant]12runs       = 6413depth      = 5014fail_on_revert = false15call_override = true1617[profile.ci.fuzz]18runs       = 641920[profile.ci.invariant]21runs       = 822depth      = 202324[profile.nightly.invariant]25runs       = 51226depth      = 200

01# 1) invariant 실행해 카운터 예시 확보02forge test --match-test invariant_totalSupplyEqualsTrackedBalances -vvv0304# 2) 출력에 나온 sequence 를 복사해 새 테스트 함수에 박는다05# 3) 단일 시드 재현 검증06forge test --match-test testRegression_FreezeBypassViaTransferFrom --seed 0xdeadbeef -vvv