Web3 & DApp Development Fundamentals · Aula

Escrita de testes

Mocha e Chai

Escrita de testes é uma aula grátis de Web3 & DApp Development Fundamentals no CoddyKit. Esta é a aula 1 de 4. Você pode ler a aula completa abaixo gratuitamente — depois pratica ao vivo no navegador com um editor de código integrado e um tutor de IA 24/7. Faz parte do caminho de aprendizado de Web3 & DApp Development Fundamentals, e seu progresso é sincronizado entre a web e o app CoddyKit. O curso de Web3 & DApp Development Fundamentals inclui 4 aulas no total.

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Why Test Contracts

Smart contracts are immutable once deployed and often hold real value. A single bug can be unrecoverable, so thorough testing is essential.

Catch logic errors before deployment.
Document expected behavior.
Guard against regressions when refactoring.

Mocha and Chai

Hardhat uses Mocha as the test runner and Chai for assertions, both included in the Toolbox.

describe groups related tests.
it defines a single test case.
expect makes assertions about values.

Tests live in the test/ folder.

A First Test File

A basic test imports ethers and Chai, then deploys and checks the contract:

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

describe("Greeter", function () {
  it("returns the initial greeting", async function () {
    const Greeter = await ethers.getContractFactory("Greeter");
    const greeter = await Greeter.deploy();
    expect(await greeter.greeting()).to.equal("Hello, Hardhat");
  });
});

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

describe("Greeter", function () {
  it("returns the initial greeting", async function () {
    const Greeter = await ethers.getContractFactory("Greeter");
    const greeter = await Greeter.deploy();
    expect(await greeter.greeting()).to.equal("Hello, Hardhat");
  });
});

Running Tests

Run the whole suite with:

npx hardhat test

Hardhat compiles contracts first, spins up a fresh in-process network, and reports passing and failing tests. You can pass a path to run just one file.

npx hardhat test

Async and await

Almost every contract interaction is asynchronous because it talks to the network. Always await deployments and calls:

it("works", async function () {
  const c = await Factory.deploy();
  await c.waitForDeployment();
  const value = await c.getValue();
  expect(value).to.equal(0);
});

Forgetting await is the most common cause of confusing test results.

it("works", async function () {
  const c = await Factory.deploy();
  await c.waitForDeployment();
  const value = await c.getValue();
  expect(value).to.equal(0);
});

Common Chai Matchers

Chai gives expressive matchers for assertions:

.to.equal(x) — strict equality.
.to.be.true / .to.be.false — booleans.
.to.be.gt(n) — greater than.
.to.deep.equal([...]) — array/object equality.

expect(await token.balanceOf(user)).to.equal(100);

expect(await token.balanceOf(user)).to.equal(100);

Working with Signers

getSigners returns test accounts you can use as different users:

const [owner, alice, bob] = await ethers.getSigners();
await token.connect(alice).transfer(bob.address, 50);

connect(signer) sends the next call as that account, which is key for testing access control.

const [owner, alice, bob] = await ethers.getSigners();
await token.connect(alice).transfer(bob.address, 50);

BigInt Values

Numbers on-chain are large integers. In ethers v6 they are JavaScript BigInt values. Compare them carefully:

const supply = await token.totalSupply();
expect(supply).to.equal(ethers.parseEther("1000"));

Use parseEther and formatEther to convert between human and on-chain units.

const supply = await token.totalSupply();
expect(supply).to.equal(ethers.parseEther("1000"));

Setup with beforeEach

Use beforeEach to deploy a fresh contract for every test, ensuring isolation:

let token;
beforeEach(async function () {
  const Token = await ethers.getContractFactory("Token");
  token = await Token.deploy();
});

Each it then starts from a clean, identical state.

let token;
beforeEach(async function () {
  const Token = await ethers.getContractFactory("Token");
  token = await Token.deploy();
});

Reading Test Output

A green checkmark means the test passed; a red cross with a diff shows what failed. Mocha prints the describe and it labels, so write descriptive names:

Good: it("reverts when caller is not owner")
Vague: it("test1")

Running a Single Test

While developing you often want to focus on one test. Use Mocha's .only:

it.only("reverts when not owner", async function () {
  // only this test runs
});

You can also run a single file with npx hardhat test test/Token.js. Remember to remove .only before committing.

it.only("reverts when not owner", async function () {
  // only this test runs
});

Quick Check

Test your understanding of writing contract tests.

Recap

You learned to write contract tests.

Hardhat uses Mocha (describe/it) and Chai (expect).
Tests live in test/ and run with npx hardhat test.
Always await async contract calls.
getSigners + connect simulate different users.
On-chain numbers are BigInt; use parseEther/formatEther and beforeEach for clean setup.

Perguntas Frequentes

A aula “Escrita de testes” é grátis?

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Preciso ter experiência prévia para começar Web3 & DApp Development Fundamentals?

Nenhuma experiência prévia é necessária. Web3 & DApp Development Fundamentals no CoddyKit é estruturado para alunos iniciantes até avançados, então você pode começar aqui ou desde o início e aprender no seu ritmo. Esta é a aula 1 de 4.

Quanto tempo leva a aula “Escrita de testes”?

A maioria das aulas CoddyKit leva cerca de 5–10 minutos. Cada uma é compacta e interativa, então você faz progresso constante e retoma exatamente de onde parou entre web e app.

Posso escrever e executar código nesta aula de Web3 & DApp Development Fundamentals?

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