Here’s an article on how to pass arguments to a contract file in Solidity, along with an example of what might go wrong when testing a contract.

Passing Arguments to a Contract File in Solidity

When writing smart contracts in Solidity, one common task is passing arguments from the application that deployed the contract. This can be done using function calls on the contract instance or by modifying the contract code itself.

In this article, we’ll cover how to pass arguments to a contract file and troubleshoot when testing a contract returns 0.

Passing Arguments in the Deployed Contract

First, let’s assume that your deployed contract is HelioToken with an event emitted called TotalSupply. To call this function from another contract, you need to create an instance of HelioToken. However, it seems like you’re missing some code, so I’ll provide a basic example.

// 2_deploy_contract.js


const HelioToken = artifacts.require("HelioToken");

module.exports = function (deploy) {

  const intialSupply = 1000000;

  deployer.deploy(HelioToken, intialSupply);


  // Now you can call the TotalSupply event

  HelioToken.totalSupply().then(totalSupply => {

    console.log("Total Supply: %s", totalSupply);

  });

};

Testing a Contract with Passing Arguments

Now that we’ve deployed our contract and passed an argument, let’s test it using Truffle’s built-in testing environment. We’ll create two contracts: HelioToken and ContractWithPassedArgument.

// HelioToken.sol


pragma solidity ^0.6.0;


contract HelioToken {

  mapping(address => uint256) public balances;


  function totalSupply() external view returns (uint256) {

    return balances[msg.sender];

  }


  function addBalance(uint256 amount, address who) public {

    balances[who] += amount;

  }

}

// ContractWithPassedArgument.sol


pragma solidity ^0.6.0;


contract ContractWithPassedArgument {

  uint256 public passedAmount = 0;

  mapping(address => uint256) public passedBalances;


  function addBalance(uint256 amount, address who) public {

    passedBalances[who] += amount;

  }


  function totalSupply() external view returns (uint256) {

    return passedBalances[msg.sender];

  }

}

Now let’s test our contracts.

// 1_deploy_contract.js


const HelioToken = artifacts.require("HelioToken"");

ContractWithPassedArgument calldata contractWithPassedArgument;


module.exports = function (deploy) {

  const intialSupply = 1000000;

  deployer.deploy(HelioToken, intialSupply);


  // Now we can test our contract

  contractWithPassedArgument.addBalance(intialSupply, msg.sender);

}

In the above example, when you run 1_deploy_contract.js, it will deploy two contracts: HelioToken and ContractWithPassedArgument. Then, it adds a certain amount of HelioToken to the ContractWithPassedArgument instance.

Troubleshooting Passing Arguments

Now that we’ve tested our contract, let’s troubleshoot why it returns 0 when testing. There are several reasons for this:

• Missing deployment code: If your deployed contracts don’t have the totalSupply() and addBalance() functions defined correctly, or if they’re not accessible from another contract, then passing arguments won’t work.

• Incorrect event handling: Make sure that you’ve called the correct events on the HelioToken instance. In this example, we’ve passed an argument to HelioToken.totalSupply(), but it’s actually an external call.

To fix these issues:

• Check your deployed contracts’ code for any errors or inconsistencies.

• Verify that you’re calling the correct functions and passing arguments correctly.

• Make sure that both contracts are accessible from another contract, like in our example.

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