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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πŸ‘· Welcome to Hardhat v2.0.3 πŸ‘·β€

? 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
β”œβ”€β”€ contracts
β”‚   └── Greeter.sol
β”œβ”€β”€ node_modules
β”œβ”€β”€ scripts
β”‚   └── sample-script.js
β”œβ”€β”€ test
β”‚   └── sample-test.js
β”œβ”€β”€ .gitattributs
β”œβ”€β”€ .gitignore
β”œβ”€β”€ 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.

βœ“ 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!'
    βœ“ 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:

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

2 passing (2s)

Congrats! You made it πŸ™‚

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.