What are the differences of Foundry vm.prank vs vm.broadcast

Question

What are the differences of Foundry vm.prank vs vm.broadcast

Answer 1

prank sets msg.sender to the address provided to it.

broadcast actually creates transactions that can then be signed and sent on chain.

broadcast can be used to deploy contracts inside of scripts, for example I can grab my private key from my .env file and then deploy a contract with it.

contract NFTScript is Script {

    function run() public {
        vm.startBroadcast(vm.envUint("PRIVATE_KEY"));
        NFT nft = new NFT("NonFun", "NFT");
        console2.log(address(nft));
        vm.stopBroadcast();
    }
}

prank can be used to ensure some tests pass, for example, any function that restricts the caller to a specific address.

 function withdraw() public {
     require(msg.sender == owner);
}

This test would pass a function call to withdraw:

function testCall() public {
vm.prank(owner);
myContract.withdraw(); 
}

Meanwhile, this test would also pass:

function testBroadcast() public {
        vm.startBroadcast(owner);
        claim.withdraw();
        vm.stopBroadcast();
    }

Answer 2

vm.prank: Sets the next call's msg.sender to be the input address

vm.broadcast: Using the address that calls the test contract, has the next call (at this call depth only) create a transaction that can later be signed and sent onchain