Foundry Setup – Troubleshooting Solc Installation Issues

When you want to withdraw and the signing account is the deployer and test contract itself (it's the same), like you have, then you need to give the contract TestContract is Test the ability to receive ether, like you would do for any other contract. Add the following to the contracts body.

// Function to receive Ether. msg.data must be empty
receive() external payable {}

// Fallback function is called when msg.data is not empty
fallback() external payable {}

Other than that you could use vm.prank and specify an EOA which is capable of receiving ether anyway. Remember you would need to use vm.prank for contract deployment (owner is not test contract but EOA and before withdraw function execution)

To construct signatures from (v,r,s), you can use:

bytes memory test = abi.encodePacked(r, s, v);
console.logBytes(test);