Testing of Smart Contract

Important terminologies to understand:

• describe: A describe block is used for organizing test cases in logical groups of tests. For example, we want to group all the tests for a specific class.
• it: Defining tests using its function.
• beforeEach: Used for code reusability and reducing redundancy of code. Create a token.js file in the test directory( folder ).

Paste the below code into the token.js file:

In your command prompt or terminal run npx hardhat test, and the following output is expected:

 Token contract   
✓ Deployment should assign the total supply of tokens to the owner (654ms) 
1 passing (663ms)

Which means the test has been passed.

 const [owner] = await ethers.getSigners();

In ethers.js, a Signer is an object that represents an Ethereum account. Transactions are sent to contracts and other accounts using this method. We’re obtaining a list of the accounts in the node we’re connected to, which is Hardhat Network in this case, and we’re just saving the first one. The global scope includes the ethers variable. If you prefer that your code be always explicit, you may add the following line at the top:

const { ethers } = require("hardhat");

const Token = await ethers.getContractFactory("Token");

A ContractFactory is used to create an instance of a token contract. Token here is just the instance.

const hardhatToken = await Token.deploy();

Calling the deploy() function on a ContractFactory instance will start the deployment process and returns a Promise. This object that gets created has a method for each of your smart contract functions.

const ownerBalance = await hardhatToken.balanceOf(owner.address);

After deploying the contract, contract methods on hardhatToken can be easily called. By calling the balanceOf() method we can extract the owner’s account balance.

It is important to understand that the account that deploys the token gets its entire supply. And by default instances are connected to the first signer.

expect(await hardhatToken.totalSupply()).to.equal(ownerBalance);

Here it is IMPORTANT to note that the total supply and owner’s balance should be equal. Therefore to check this, we wrote the above code statement, which will tell you whether the contract is correctly deployed or not.
To do this we’re using Chai which is a popular JavaScript assertion library. These asserting functions are called “matchers“, and the ones we’re using here come from the @nomicfoundation/hardhat-chai-matchers plugin, which extends Chai with many matchers useful to test smart contracts.

Using a Different Account

To test your code by sending a transaction from an account (or Signer in ethers.js terminology) other than the default one, you can use the connect() method on your ethers.js Contract object to connect it to a different account, like this:

Full Test Suite

The below Code is the full test suite for Token.sol with other added information and the tests to be performed are structured in comprehended format.

Run npx hardhat test in your command prompt/ terminal. The output of npx hardhat test should look like this:

Note : npx hardhat test would automatically compile the last updated code.

Debugging

Debugging of solidity smart contracts is possible by logging messages by calling console.log() from solidity code while running smart contracts and tests on Hardhat Network. Hardhat provides a console.sol module which makes it possible to log messages from solidity code. To do so, you just need to import hardhat/console.sol. This is how it should look like:

Then you can simply add console.log to solidity functions similar to using it in Javascript. Here we are using it in the transfer() function.

Logging outputs will be reflected when you run your tests:

Public Blockchains like Ethereum are immutable, it is difficult to update the code of a smart contract once it has been deployed. To guarantee security, smart contracts must be tested before they are deployed to Mainnet. There are several strategies for testing contracts, but a test suite comprised of various tools and approaches is suitable for detecting both minor and significant security issues in contract code.