AngryCalculator.sol

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.13;

import "lib/solidity-bytes-utils/contracts/BytesLib.sol";

error Sum(uint256 total);

contract AngryCalculator {
    using BytesLib for bytes;

    function _addNumbers(uint256 number1, uint256 number2) external pure {
        revert Sum(number1 + number2);
    }

    function calculate(
        uint256 number1,
        uint256 number2
    ) public view returns (uint256 sum) {
        try this._addNumbers(number1, number2) {} catch (bytes memory err) {
            return err.toUint256(4);
        }
    }
}

AngryCalculator.t.sol

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.13;

import "forge-std/Test.sol";
import "forge-std/console.sol";
import "lib/solidity-bytes-utils/contracts/BytesLib.sol";

import "../src/AngryCalculator.sol";

contract AngryCalculatorTest is Test {
    using BytesLib for bytes;

    AngryCalculator public ac;

    function setUp() public {
        ac = new AngryCalculator();
    }

    function testSum() public {
        uint256 res = ac.calculate(31, 38);
        assertEq(res, 69);
    }
}