solidity/test/libsolidity/semanticTests/modifiers/function_modifier_multi_invocation.sol

contract C {
    modifier repeat(bool twice) {
        if (twice) _;
        _;
    }

    function f(bool twice) public repeat(twice) returns (uint256 r) {
        r += 1;
    }
}

// ----
// f(bool): false -> 1
// f(bool): true -> 2