i want to ask this unit test about "fundme"：why does the last assert add 1?

[lc345]

function testWithdrawFromMultipleFunders() public funded skipZkSync {
uint160 numberOfFunders = 10;
uint160 startingFunderIndex = 2;
for (
uint160 i = startingFunderIndex;
i < numberOfFunders + startingFunderIndex;
i++
) {
// we get hoax from stdcheats
// prank + deal
hoax(address(i), STARTING_USER_BALANCE);
fundMe.fund{value: SEND_VALUE}();
}

    uint256 startingFundMeBalance = address(fundMe).balance;
    uint256 startingOwnerBalance = fundMe.getOwner().balance;

    vm.startPrank(fundMe.getOwner());
    fundMe.withdraw();
    vm.stopPrank();

    assert(address(fundMe).balance == 0);
    assert(
        startingFundMeBalance + startingOwnerBalance ==
            fundMe.getOwner().balance
    );
    assert(
        (numberOfFunders + 1) * SEND_VALUE ==
            fundMe.getOwner().balance - startingOwnerBalance
    );
}

[KMean]

@lc345 because we are using the funded modifier which prank the USER and send some funds to the contract

 modifier funded() {
        vm.prank(USER);
        fundMe.fund{value: SEND_VALUE}();
        assert(address(fundMe).balance > 0);
        _;
    }

so we need to count for that in the assertion. In fact if you log the amount of USER contribution you will see it does indeed exist.

function testWithdrawFromMultipleFunders() public funded skipZkSync {
        uint160 numberOfFunders = 10;
        uint160 startingFunderIndex = 2;
        console.log("USER contribution:", fundMe.getAddressToAmountFunded(USER));
        for (uint160 i = startingFunderIndex; i < numberOfFunders + startingFunderIndex; i++) {
            // we get hoax from stdcheats
            // prank + deal
            hoax(address(i), STARTING_USER_BALANCE);
            fundMe.fund{value: SEND_VALUE}();
        }

        uint256 startingFundMeBalance = address(fundMe).balance;
        uint256 startingOwnerBalance = fundMe.getOwner().balance;

        vm.startPrank(fundMe.getOwner());
        fundMe.withdraw();
        vm.stopPrank();

        assert(address(fundMe).balance == 0);
        assert(startingFundMeBalance + startingOwnerBalance == fundMe.getOwner().balance);
        assert((numberOfFunders + 1) * SEND_VALUE == fundMe.getOwner().balance - startingOwnerBalance);
    }

forge test --mt testWithdrawFromMultipleFunders -vvvv
[⠊] Compiling...
[⠢] Compiling 1 files with Solc 0.8.19
[⠆] Solc 0.8.19 finished in 1.10s
Compiler run successful!

Ran 1 test for test/unit/FundMeTest.t.sol:FundMeTest
[PASS] testWithdrawFromMultipleFunders() (gas: 601676)
Logs:
  ⚠️ You have deployed a mock contract!
  Make sure this was intentional
  USER contribution: 100000000000000000

[lc345]

i got it, thank you very much. i do not notice the funded modifier.