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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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:
-
constructor – where we declare a string type variable called
greeting
, -
function greet – a function that will return the
greeting
when called, -
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.