NestJS Enterprise Backend APIs · Aula

Testes unitários de contratos inteligentes

Aprenda a escrever testes unitários abrangentes para seus contratos Solidity, garantindo sua correção, segurança e comportamento esperado.

Testes unitários de contratos inteligentes é uma aula grátis de NestJS Enterprise Backend APIs no CoddyKit. Esta é a aula 4 de 6. 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 NestJS Enterprise Backend APIs, e seu progresso é sincronizado entre a web e o app CoddyKit. O curso de NestJS Enterprise Backend APIs inclui 6 aulas no total.

Partes desta aula ainda não foram traduzidas e aparecem em inglês.

Unit Testing Smart Contracts

Welcome to unit testing for smart contracts! This lesson will guide you through writing effective tests for your Solidity code.

Unit tests are crucial in traditional software development, but they are absolutely vital in the blockchain world due to the immutable nature of smart contracts and the financial value they often secure.

Why Test Smart Contracts?

Unlike regular applications, smart contracts, once deployed, cannot be easily changed. Bugs can lead to significant financial losses or system failures.

Immutability: Deployed contracts are permanent.
High Stakes: Often manage valuable assets.
Security: Protect against vulnerabilities.
Reliability: Ensure functions behave as expected.
Gas Costs: Bugs can waste user funds.

Thorough testing helps catch issues before deployment.

Introducing Hardhat for Testing

Hardhat is a popular Ethereum development environment that includes a powerful testing framework. It provides a local Ethereum network (Hardhat Network) for fast, isolated testing.

Local Network: Deploy and test without real gas fees.
Ethers.js Integration: Interact with contracts using a familiar JavaScript library.
Debugging: Tools for understanding transaction failures.

We'll use Hardhat to write our unit tests.

Basic Contract for Testing

Let's start with a simple Solidity contract that we'll use for our unit tests. This Counter contract allows us to increment, decrement, and get a count.

Copy and save this as contracts/Counter.sol in your Hardhat project.

pragma solidity ^0.8.0;

contract Counter {
  uint public count;

  constructor() {
    count = 0;
  }

  function increment() public {
    count += 1;
  }

  function decrement() public {
    require(count > 0, "Count cannot be negative");
    count -= 1;
  }

  function getCount() public view returns (uint) {
    return count;
  }
}

Setting Up Your Test File

Hardhat expects test files to be in the test/ directory. We'll use Mocha for our test runner and Chai for assertions, both integrated with Hardhat.

describe(): Groups related tests.
it(): Defines an individual test case.
beforeEach(): Runs before each test in a describe block, useful for setup.

Let's create a file named test/Counter.js.

Deploying Your Contract in Tests

Before we can test our contract's functions, we need to deploy it to our local Hardhat network. The beforeEach block is perfect for this, ensuring a fresh deployment for every test.

Try running this test file. It should pass if your contract is correctly set up.

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

describe("Counter", function () {
  let counter; // Declare 'counter' to be accessible in all tests

  beforeEach(async function () {
    const CounterFactory = await ethers.getContractFactory("Counter");
    counter = await CounterFactory.deploy();
    await counter.deployed(); // Wait for deployment to be confirmed
  });

  // A simple test to confirm deployment
  it("Should confirm the contract is deployed", async function () {
    expect(counter.address).to.not.be.null;
  });
});

Testing Initial State

The first thing to test is if our contract's initial state is correct. Our Counter contract's count should start at 0.

We use expect() from Chai to make assertions about our contract's behavior. to.equal() checks for equality.

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

describe("Counter", function () {
  let counter;

  beforeEach(async function () {
    const CounterFactory = await ethers.getContractFactory("Counter");
    counter = await CounterFactory.deploy();
    await counter.deployed();
  });

  it("Should return the initial count of 0", async function () {
    expect(await counter.getCount()).to.equal(0);
  });

  it("Should confirm the contract is deployed", async function () {
    expect(counter.address).to.not.be.null;
  });
});

Testing State Changes (Increment)

Now let's test a function that changes the contract's state. After calling increment(), we expect the count to increase by one.

Remember that state-changing functions need to be awaited because they involve a transaction on the blockchain.

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

describe("Counter", function () {
  let counter;

  beforeEach(async function () {
    const CounterFactory = await ethers.getContractFactory("Counter");
    counter = await CounterFactory.deploy();
    await counter.deployed();
  });

  it("Should return the initial count of 0", async function () {
    expect(await counter.getCount()).to.equal(0);
  });

  it("Should increment the count by 1", async function () {
    await counter.increment();
    expect(await counter.getCount()).to.equal(1);
  });

  it("Should confirm the contract is deployed", async function () {
    expect(counter.address).to.not.be.null;
  });
});

Testing Function Logic (Decrement)

We can also test the decrement() function. For this, we first need to increment the counter to ensure count is greater than zero.

This shows how tests can involve a sequence of operations to reach a desired state before asserting the outcome.

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

describe("Counter", function () {
  let counter;

  beforeEach(async function () {
    const CounterFactory = await ethers.getContractFactory("Counter");
    counter = await CounterFactory.deploy();
    await counter.deployed();
  });

  it("Should return the initial count of 0", async function () {
    expect(await counter.getCount()).to.equal(0);
  });

  it("Should increment the count by 1", async function () {
    await counter.increment();
    expect(await counter.getCount()).to.equal(1);
  });

  it("Should decrement the count by 1", async function () {
    await counter.increment(); // First increment to make count > 0
    await counter.decrement();
    expect(await counter.getCount()).to.equal(0);
  });

  it("Should confirm the contract is deployed", async function () {
    expect(counter.address).to.not.be.null;
  });
});

Testing for Expected Reverts

Smart contracts often use require() or revert() to enforce conditions. It's vital to test that these conditions correctly trigger a revert when violated.

Chai's to.be.revertedWith() assertion allows us to check for specific error messages.

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

describe("Counter", function () {
  let counter;

  beforeEach(async function () {
    const CounterFactory = await ethers.getContractFactory("Counter");
    counter = await CounterFactory.deploy();
    await counter.deployed();
  });

  it("Should return the initial count of 0", async function () {
    expect(await counter.getCount()).to.equal(0);
  });

  it("Should increment the count by 1", async function () {
    await counter.increment();
    expect(await counter.getCount()).to.equal(1);
  });

  it("Should decrement the count by 1", async function () {
    await counter.increment();
    await counter.decrement();
    expect(await counter.getCount()).to.equal(0);
  });

  it("Should revert if decrementing from zero", async function () {
    await expect(counter.decrement()).to.be.revertedWith("Count cannot be negative");
  });

  it("Should confirm the contract is deployed", async function () {
    expect(counter.address).to.not.be.null;
  });
});

Quick Check: Test Assertions

What are the key benefits of using expect().to.be.revertedWith("...") in smart contract unit tests?

Recap: Unit Testing Power

In this lesson, you've learned the critical importance of unit testing for smart contracts and how to write effective tests using Hardhat, Mocha, and Chai.

Smart contracts require rigorous testing due to their immutability.
Hardhat provides a powerful local environment for fast testing.
You can test initial states, state changes, function logic, and expected reverts.

Mastering unit testing is a fundamental skill for any secure and reliable DApp developer.

Perguntas Frequentes

A aula “Testes unitários de contratos inteligentes” é grátis?

Sim — o texto completo de “Testes unitários de contratos inteligentes” é grátis para ler aqui na web. Para praticá-la interativamente (um editor de código integrado e um tutor de IA 24/7) e desbloquear o restante do curso de NestJS Enterprise Backend APIs, atualize para CoddyKit PRO. O curso de NestJS Enterprise Backend APIs inclui 6 aulas no total.

O que vou aprender em “Testes unitários de contratos inteligentes”?

Aprenda a escrever testes unitários abrangentes para seus contratos Solidity, garantindo sua correção, segurança e comportamento esperado. Você pratica NestJS Enterprise Backend APIs com código prático que executa diretamente no navegador, e um tutor de IA 24/7 responde suas dúvidas enquanto trabalha na aula.

Preciso ter experiência prévia para começar NestJS Enterprise Backend APIs?

Nenhuma experiência prévia é necessária. NestJS Enterprise Backend APIs 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 4 de 6.

Quanto tempo leva a aula “Testes unitários de contratos inteligentes”?

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 NestJS Enterprise Backend APIs?

Sim. Cada aula de NestJS Enterprise Backend APIs inclui um editor de código integrado, então você escreve e executa código real direto no navegador e recebe feedback de IA instantaneamente — nenhuma configuração local necessária.

Todas as aulas deste curso

Testes Unitários e de Ponta a Ponta
Frameworks Hardhat e Truffle
Testes de Desempenho de APIs
Testes unitários de contratos inteligentes
Conteinerização e Kubernetes
Implantação em redes de teste e na rede principal

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