Waffle say hello world tutorial with hardhat and ethers

waffle

smart contracts

solidity

testing

hardhat

ethers.js

basic

️MiZiet

October 16, 2020

1 minute read

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

npm init

and installing required packages:

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

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

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Select Create a sample project

Our project's structure should look like this:

1MyWaffleProject
2├── contracts
3│   └── Greeter.sol
4├── node_modules
5├── scripts
6│   └── sample-script.js
7├── test
8│   └── sample-test.js
9├── .gitattributs
10├── .gitignore
11├── hardhat.config.js
12└── package.json
13
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Now let's talk about some of these files:

Greeter.sol - our smart contract writen in solidity;

1contract Greeter {
2string greeting;
3
4constructor(string memory _greeting) public {
5console.log("Deploying a Greeter with greeting:", _greeting);
6greeting = _greeting;
7}
8
9function greet() public view returns (string memory) {
10return greeting;
11}
12
13function setGreeting(string memory _greeting) public {
14console.log("Changing greeting from '%s' to '%s'", greeting, _greeting);
15greeting = _greeting;
16}
17}
18
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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

1describe("Greeter", function () {
2  it("Should return the new greeting once it's changed", async function () {
3    const Greeter = await ethers.getContractFactory("Greeter")
4    const greeter = await Greeter.deploy("Hello, world!")
5
6    await greeter.deployed()
7    expect(await greeter.greet()).to.equal("Hello, world!")
8
9    await greeter.setGreeting("Hola, mundo!")
10    expect(await greeter.greet()).to.equal("Hola, mundo!")
11  })
12})
13
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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().

1it("Should revert when passing an empty string", async () => {
2  const Greeter = await ethers.getContractFactory("Greeter")
3  const greeter = await Greeter.deploy("Hello, world!")
4
5  await greeter.deployed()
6  await expect(greeter.setGreeting("")).to.be.revertedWith(
7    "Greeting should not be empty"
8  )
9})
10
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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

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Let's implement this functionality into our smart contract:

1require(bytes(_greeting).length > 0, "Greeting should not be empty");
2
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Now, our setGreeting function looks like this:

1function setGreeting(string memory _greeting) public {
2require(bytes(_greeting).length > 0, "Greeting should not be empty");
3console.log("Changing greeting from '%s' to '%s'", greeting, _greeting);
4greeting = _greeting;
5}
6
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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.

For more great chai matchers to test your smart contracts, check official Waffle's docs.

Last edit: , Invalid DateTime

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