Truffle test in solidity with sending value - solidity

Question

duplicating my question from SA:
I have a simple contract with public function, that can receive value and do something based on that value:
pragma solidity >= 0.8.0 < 0.9.0;
contract ContractA {
uint public boughtItems = 0;
uint price = 10;
address [] buyers;
function buySomething() public payable {
require(msg.value >= price, "Sent value is lower");
boughtItems++;
buyers.push(msg.sender);
}
}
and in test folder of my Truffle project I have test contract:
pragma solidity >=0.8.0 <0.9.0;
import "truffle/Assert.sol";
import "truffle/DeployedAddresses.sol";
import "../contracts/TicketsRoutes.sol";
contract TestTicketsRoutes {
ContractA instance;
address account1 = 0xD8Ce37FA3A1A61623705dac5dCb708Bb5eb9a125;
function beforeAll() public {
instance = new ContractA();
}
function testBuying() public {
//Here I need to invoke buySomething with specific value from specific address
instance.buySomething();
Assert.equal(instance.boughtItems, 1, "Routes amount is not equal");
}
}
How do I invoke function of ContractA in my TestContractA with passing value and sender?

Answer 1

You can use the low-level call() Solidity function to pass a value.
(bool success, bytes memory returnedData) = address(instance).call{value: 1 ether}(
abi.encode(instance.buySomething.selector)
);
But, in order to execute the buySomething() function from a different sender, you need to send it from a different address than the TestTicketsRoutes deployed address.
So you'll need to change your approach and perform the test from an off-chain script (instead of the on-chain test contract) that allows you to sign the transaction from a different sender. Since you tagged the question truffle, here's an example of executing a contract function using the Truffle JS suite (docs).
const instance = await MyContract.at(contractAddress);
const tx = await instance.buySomething({
from: senderAddress,
value: web3.toWei(1, "ether")
});