Reading contract balances with Waffle? - unit-testing

Question

Context
After adopting a waffle example I'm experiencing some difficulties in reading out the balances of the contracts that are made using a unit test in Waffle.
Test file
import {expect, use} from 'chai';
import {Contract, utils, Wallet} from 'ethers';
import {deployContract, deployMockContract, MockProvider, solidity} from 'ethereum-waffle';
import IERC20 from '../build/IERC20.json';
import AmIRichAlready from '../build/AmIRichAlready.json';
import SolveContract from '../build/SolveContract.json';
import RandomNumberConsumer from '../build/RandomNumberConsumer.json';
use(solidity);
describe('Am I Rich Already', () => {
// Declare contracts
let mockERC20: Contract;
let askRootContract: Contract;
let solveRootContract: Contract;
let vrfContract: Contract;
// Declare wallets
let mockWallet: Wallet;
let askRootWallet: Wallet;
let solveRootWallet: Wallet;
let vrfWallet: Wallet;
beforeEach(async () => {
// generate random wallets or random origin
//const [mockWallet, askRootWallet, solveRootWallet, vrfWallet] = Wallet.createRandom();
//const original = Wallet.createRandom();
// specify wallet balances
const provider = new MockProvider(
{
ganacheOptions: {
// The private key is used to generate the four respective wallet addresses.
accounts: [
{balance: '16862680000000000001', secretKey: '0x706618637b8ca922f6290ce1ecd4c31247e9ab75cf0530a0ac95c0332173d7c1'},
{balance: '16862680000000000002', secretKey: '0x706618637b8ca922f6290ce1ecd4c31247e9ab75cf0530a0ac95c0332173d7c2'},
{balance: '16862680000000000003', secretKey: '0x706618637b8ca922f6290ce1ecd4c31247e9ab75cf0530a0ac95c0332173d7c3'},
{balance: '16862680000000000004', secretKey: '0x706618637b8ca922f6290ce1ecd4c31247e9ab75cf0530a0ac95c0332173d7c4'}
]
}
}
);
[mockWallet, askRootWallet, solveRootWallet, vrfWallet] = provider.getWallets();
mockERC20 = await deployMockContract(mockWallet, IERC20.abi);
askRootContract = await deployContract(askRootWallet, AmIRichAlready, [mockERC20.address]);
solveRootContract = await deployContract(solveRootWallet, SolveContract, [mockERC20.address]);
vrfContract = await deployContract(vrfWallet, RandomNumberConsumer);
});
// custom test in AskRoot contract
it('checks askRootContract address is returned correctly', async () => {
expect(await askRootContract.getAddressThis()).to.be.equal('0x82A666453d8aa239eEBE4578E83cD0988D62c83F');
});
// custom test in AskRoot contract
it('checks askRootWallet address balance is returned correctly', async () => {
expect(await askRootContract.getAddressThisBalance()).to.be.equal(9001);
});
});
Example contract
// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.4.16 <0.9.0;
// Example contract of a TestContract.
contract SolveContract {
bool forTestingPurposes; // Boolean to run test on this contract
TemplateTestContract testContract; // Create variable for the testContract which needs to be solved.
address payable owner; // Create variable for the owner which solves the test contract.
// Constructor to initialise the contract variables.
constructor(address testAddress) public payable {
testContract = TemplateTestContract(testAddress); // Initialise the testContract variable.
owner = msg.sender; // Initialise the owner of the contract to be the creator of the contract.
}
// Function to solve the testContract.
function solve() public payable returns(uint256){
testContract.differentFunctionName(owner);
return owner.balance;
}
// Example of the main function which solves the testContract.
// Calculates the squre root function.
function main(uint x) pure public returns(uint y) {
uint z = (x + 1) / 2;
y = x;
while (z < y) {
y = z;
z = (x / z + z) / 2;
}
}
// Getter function for the Ownership.
function getOwner() public view returns (address) {
return owner;
}
// Getter function for the address(this).
function getAddressThis() public view returns (address) {
return address(this);
}
// Getter function for the balance of the contract.
function getBalance() public view returns (uint) {
//return address(this).balance;
//testAddress.balance;
return owner.balance;
}
// Getter function for the forTestingPurposes boolean.
function getForTestingPurposes() public view returns (bool){
return forTestingPurposes;
}
}
// TemplateTestContract so the SolveContract knows the structure of the testContract.
abstract contract TemplateTestContract {
function differentFunctionName(address payable hunter) public virtual;
}
Test Output
1) checks askRootWallet address balance is returned correctly
AssertionError: Expected "0" to be equal 9001
at Context.it (test/AmIRichAlready.test.ts:53:76)
at process._tickCallback (internal/process/next_tick.js:68:7)
Question
How can I (set) and read out the balance of the wallet address of a particular contract in a Waffle test?

Answer 1

Your test script is calling function getAddressThisBalance(), but this function is not defined in the contract.
Different JSON-RPC wrappers act differently when performing calls (read-only, without transaction) to non-existing contract functions. Some return undefined, some throw an exception, and it seems that Waffle returns a value that can be typecasted to 0.
Solution:
Unify the contract function getBalance() and the JS snippet calling getAddressThisBalance(). E.g. change the JS call to getBalance().
Uncomment the line return address(this).balance; in your getBalance() contract function. This expression returns the current balance of the contract.