I've been working with the voting contract example, and been unit testing it with Truffle and Javascript. So far I have managed to test every function from my contract with success. But when i tried to retrieve the candidateList property it didn't work. Part of the testing file

it('returns every candidate', async () => {
    let fundRaise = await Voting.new(['Alice', 'Bob', 'Rick']);

    const cands = await voting.candidateList();

When i execute the above test, truffle shows the following

1) Contract: Voting returns every candidate:
 Error: Invalid number of arguments to Solidity function
  at Object.InvalidNumberOfSolidityArgs (/usr/lib/node_modules/truffle/build/webpack:/~/web3/lib/web3/errors.js:25:1)
  at SolidityFunction.validateArgs (/usr/lib/node_modules/truffle/build/webpack:/~/web3/lib/web3/function.js:74:1)
  at SolidityFunction.toPayload (/usr/lib/node_modules/truffle/build/webpack:/~/web3/lib/web3/function.js:90:1)
  at SolidityFunction.call (/usr/lib/node_modules/truffle/build/webpack:/~/web3/lib/web3/function.js:131:1)
  at SolidityFunction.execute (/usr/lib/node_modules/truffle/build/webpack:/~/web3/lib/web3/function.js:260:1)
  at /usr/lib/node_modules/truffle/build/webpack:/~/truffle-contract/contract.js:135:1
  at new Promise (<anonymous>)
  at /usr/lib/node_modules/truffle/build/webpack:/~/truffle-contract/contract.js:126:1
  at <anonymous>
  at process._tickDomainCallback (internal/process/next_tick.js:228:7)

What i don't get is why if the getter function is generated automatically, web3 is throwing this message. I have Truffle v4.1.7 (core: 4.1.7); Solidity v0.4.23 (solc-js); Geth/v1.8.1-stable-1e67410e/linux-amd64/go1.9.4"; web3 version api: '0.20.6',

Below is the contract file as well, as the testing file.

pragma solidity ^0.4.17;

contract Voting {

mapping (bytes32 => uint8) public votesReceived;
bytes32[] public candidateList;

constructor(bytes32[] _candidates) public {
    candidateList = _candidates;

function voteForCandidate(bytes32 _name) public returns (uint8) {
    votesReceived[_name] += 1;
    //return votesReceived[_name];
    return totalVotesFor(_name);

function validateCandidate(bytes32 _name) view public returns (bool){
    for (uint8 i = 0; i < candidateList.length; i++) {
        if(candidateList[i] == _name){
            return true;
    return false;

function totalVotesFor(bytes32 name) view public returns (uint8){
    return votesReceived[name];

function addCandidate(bytes32 _name) public returns (bool) {
    return validateCandidate(_name);

const assert = require('assert');
var Voting = artifacts.require("Voting");

This is the testing file:

contract('Voting', function(accounts) {

let voting;

beforeEach(async () => {
    voting = await Voting.deployed();

it('votes for valid candidate', async () => {

    const voto = await voting.voteForCandidate.call('Andrea');

    assert.equal(voto.toNumber(),1, 'Cannot vote for valid candidate');

it('Does not vote for invalid candidate', async () => {
    const voto = await voting.voteForCandidate.call('Bacilio');

    assert.equal(voto.toNumber(), 0, 'Allowed to vote for invalid candidate');

it('Adds new candidate', async () => {
    const voto = await voting.addCandidate.call('Segismundo');
    assert.equal(voto, true, 'Did not allow to add new candidate');

it('allows to obtain votes casted for a candidate', async () => {

    const expected_votes = 2;

    //vote twice for the same candidate
    await voting.voteForCandidate('Roberto');
    await voting.voteForCandidate('Roberto');

    let casted_votes = await voting.totalVotesFor.call('Roberto');
    assert.equal(casted_votes.toNumber(), expected_votes, 'Did not got casted votes')


it('returns every candidate', async () => {
    let fundRaise = await Voting.new(['Segismundo', 'Ocatvia']);

    const cands = await voting.candidateList();


1 Answer 1


In your Solidity code, add:

function candidateListLength() external view returns (uint) {
    return candidateList.length;

In your Javascript code add:

let cands = [];
let length = Number(await voting.candidateListLength());
for (let i = 0; i < length; i++)
    cands.push(await voting.candidateList(i));
  • It worked, thanks! Just to be clear, whenever you want to access a contract's array variable. You must provide a specific index to obtain, getting the whole array is not supported?
    – Roberto C.
    May 8, 2018 at 6:15

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