Waffle with Hardhat and Ethers

Intermediate

 

Waffle with Hardhat and Ethers

In this Waffle tutorial, we will learn how to set up a simple “Hello world” smart contract project, using hardhat and ethers.js. Then we will learn how to add a new functionality to our smart contract and how to test it with Waffle.

Let’s start with creating new project:

yarn init

or

npm init

and installing required packages:

yarn add -D hardhat @nomiclabs/hardhat-ethers ethers @nomiclabs/hardhat-waffle ethereum-waffle chai

or

npm install -D hardhat @nomiclabs/hardhat-ethers ethers @nomiclabs/hardhat-waffle ethereum-waffle chai

Next step is creating a sample hardhat project by running npx hardhat.

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👷 Welcome to Hardhat v2.0.3 👷‍

? What do you want to do? …
❯ Create a sample project
Create an empty hardhat.config.js
Quit

Select Create a sample project

Our project’s structure should look like this:

MyWaffleProject
├── contracts
│   └── Greeter.sol
├── node_modules
├── scripts
│   └── sample-script.js
├── test
│   └── sample-test.js
├── .gitattributs
├── .gitignore
├── hardhat.config.js
└── package.json

Now let’s talk about some of these files:

  • Greeter.sol – our smart contract writen in solidity;

contract Greeter {
string greeting;

constructor(string memory _greeting) public {
console.log("Deploying a Greeter with greeting:", _greeting);
greeting = _greeting;
}

function greet() public view returns (string memory) {
return greeting;
}

function setGreeting(string memory _greeting) public {
console.log("Changing greeting from '%s' to '%s'", greeting, _greeting);
greeting = _greeting;
}
}

Our smart contract can be divided into three parts:

  1. constructor – where we declare a string type variable called greeting,
  2. function greet – a function that will return the greeting when called,
  3. function setGreeting – a function that allows us to change the greeting value.
  • sample-test.js – our tests file 
describe("Greeter", function () {
  it("Should return the new greeting once it's changed", async function () {
    const Greeter = await ethers.getContractFactory("Greeter")
    const greeter = await Greeter.deploy("Hello, world!")

    await greeter.deployed()
    expect(await greeter.greet()).to.equal("Hello, world!")

    await greeter.setGreeting("Hola, mundo!")
    expect(await greeter.greet()).to.equal("Hola, mundo!")
  })
})

Next step consists of compiling our contract and running tests:

Waffle tests use Mocha (a test framework) with Chai (an assertion library). All you have to do is run npx hardhat test and wait for the following message to appear.

✓ Should return the new greeting once it's changed

Everything looks great so far, let’s add some more complexity to our project

Imagine a situation where someone adds an empty string as a greeting. It wouldn’t be a warm greeting, right?
Let’s make sure that doesn’t happen:

We want to use solidity’s revert when someone passes an empty string. A good thing is that we can easily test this functionality with Waffle’s chai matcher to.be.revertedWith().

it("Should revert when passing an empty string", async () => {
  const Greeter = await ethers.getContractFactory("Greeter")
  const greeter = await Greeter.deploy("Hello, world!")

  await greeter.deployed()
  await expect(greeter.setGreeting("")).to.be.revertedWith(
    "Greeting should not be empty"
  )
})

Looks like our new test didn’t pass:

Deploying a Greeter with greeting: Hello, world!
Changing greeting from 'Hello, world!' to 'Hola, mundo!'
    ✓ Should return the new greeting once it's changed (1514ms)
Deploying a Greeter with greeting: Hello, world!
Changing greeting from 'Hello, world!' to ''
    1) Should revert when passing an empty string


  1 passing (2s)
  1 failing

Let’s implement this functionality into our smart contract:

require(bytes(_greeting).length > 0, "Greeting should not be empty");

Now, our setGreeting function looks like this:

function setGreeting(string memory _greeting) public {
require(bytes(_greeting).length > 0, "Greeting should not be empty");
console.log("Changing greeting from '%s' to '%s'", greeting, _greeting);
greeting = _greeting;
}

Let’s run tests again:

✓ Should return the new greeting once it's changed (1467ms)
✓ Should revert when passing an empty string (276ms)

2 passing (2s)

Congrats! You made it 🙂

Conclusion

We made a simple project with Waffle, Hardhat and ethers.js. We learned how to set up a project, add a test and implement new functionality.