Testing with ethers.js in Blockchain / Solidity - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is ethers.js used for in blockchain development?

ethers.js is a library that helps developers interact with the Ethereum blockchain. It allows you to write scripts and tests to communicate with smart contracts, send transactions, and read blockchain data.

beginner

How do you create a provider in ethers.js for testing?

<p>You create a provider using <code>ethers.providers.JsonRpcProvider</code> or use the default provider for local testing networks like Hardhat or Ganache.</p><p>Example:<br><code>const provider = new ethers.providers.JsonRpcProvider();</code></p>

beginner

What is the purpose of a signer in ethers.js tests?

A signer represents an Ethereum account that can sign transactions. In tests, signers are used to simulate different users sending transactions or interacting with contracts.

intermediate

How do you deploy a smart contract in a test using ethers.js?

<p>First, get the contract factory with <code>ethers.getContractFactory</code>. Then call <code>deploy()</code> on it and wait for deployment.</p><p>Example:<br><code>const MyContract = await ethers.getContractFactory('MyContract');<br>const contract = await MyContract.deploy();<br>await contract.deployed();</code></p>

beginner

Why is it important to use await when calling contract functions in tests?

Because blockchain interactions are asynchronous, await ensures the test waits for the transaction or call to complete before moving on. This prevents race conditions and incorrect test results.

Which ethers.js object represents an Ethereum account that can send transactions?

A Signer

B ContractFactory

C Provider

D Transaction

A Signer represents an Ethereum account that can sign and send transactions.

What method do you use to get a contract factory in ethers.js for deployment?

A ethers.getContract()

B ethers.getContractFactory()

C ethers.deployContract()

D ethers.createContract()

ethers.getContractFactory() returns a factory to deploy new contract instances.

Why do you use await when calling contract functions in tests?

A To speed up the test

B To run multiple tests at once

C To wait for the transaction to complete

D To ignore errors

await waits for the asynchronous blockchain call or transaction to finish before continuing.

Which provider is commonly used for local blockchain testing with ethers.js?

A InfuraProvider

B WebSocketProvider

C AlchemyProvider

D JsonRpcProvider

JsonRpcProvider connects to local blockchain nodes like Hardhat or Ganache for testing.

What does contract.deployed() do in ethers.js tests?

A Waits until the contract is fully deployed

B Returns the contract address

C Deploys the contract

D Compiles the contract

contract.deployed() waits for the deployment transaction to be mined and confirmed.

Explain the steps to write a simple test using ethers.js to deploy a contract and call one of its functions.

Think about how you prepare, deploy, and interact with the contract in a test.

Describe the role of providers and signers in ethers.js testing environment.

Consider who talks to the blockchain and who acts as the user.