Gas usage testing in Blockchain / Solidity - Mini Project: Build & Apply

Gas usage testing

📖 Scenario: You are developing a simple smart contract on the Ethereum blockchain. You want to measure how much gas your contract uses when calling a function that stores a number.

🎯 Goal: Build a smart contract and write a test script that measures the gas used when calling a storeNumber function.

📋 What You'll Learn

Create a smart contract with a storeNumber function that saves a number.

Write a test script that calls storeNumber and measures gas used.

Print the gas used in the test output.

💡 Why This Matters

🌍 Real World

Measuring gas usage helps developers optimize smart contracts to save money and improve performance on blockchains like Ethereum.

💼 Career

Blockchain developers must understand gas costs to write efficient contracts and manage deployment and transaction expenses.

1

Create the smart contract

Create a Solidity contract named GasTest with a public uint256 variable called storedNumber and a function storeNumber that takes a uint256 parameter called num and sets storedNumber to num.

Blockchain / Solidity

// Your Solidity contract code here

Need a hint?

Define a contract with a public variable and a function that updates it.

2

Set up the test environment

In a JavaScript test file, import ethers from hardhat and declare a variable gasTest to hold the deployed contract instance.

Blockchain / Solidity

// Import ethers and declare gasTest variable
// Your code here

Need a hint?

Use require("hardhat") to import ethers and declare a variable for the contract.

3

Deploy the contract and call the function

Write an async function main that deploys GasTest using ethers.getContractFactory, assigns it to gasTest, then calls storeNumber(42) and waits for the transaction receipt.

Blockchain / Solidity

// Write async function main to deploy and call storeNumber(42)
// Your code here

Need a hint?

Deploy the contract, then call the function and wait for the transaction receipt.

4

Print the gas used

Add a line in main to print the gas used by accessing receipt.gasUsed.toString() with console.log. Then call main() and catch errors to print them.

Blockchain / Solidity

// Print gas used here
// Your code here

// Call main and catch errors
// Your code here

Need a hint?

Use console.log to print the gas used from the receipt, then run main() with error handling.