Fork testing (mainnet fork) in Blockchain / Solidity - Mini Project: Build & Apply

Fork Testing with a Mainnet Fork

📖 Scenario: You are a blockchain developer who wants to test smart contract interactions safely without spending real money or affecting the live network. You will create a simple script to connect to a mainnet fork, check an account balance, and simulate a transaction.

🎯 Goal: Build a Python script that connects to a mainnet fork using web3.py, sets up an account, checks its balance, and simulates sending Ether to another address.

📋 What You'll Learn

Create a Web3 connection to a local mainnet fork RPC URL

Set up an account with a private key

Check the account's Ether balance

Simulate sending 0.01 Ether to another address

Print the transaction hash of the simulated transaction

💡 Why This Matters

🌍 Real World

Mainnet forks let blockchain developers test their code exactly as if on the real Ethereum network but without spending real money or risking real assets.

💼 Career

Blockchain developers and smart contract engineers use mainnet forks daily to debug, test upgrades, and verify contract behavior before deploying to live networks.

1

Set up Web3 connection to mainnet fork

Import Web3 from web3 and create a w3 variable that connects to the local mainnet fork RPC URL http://127.0.0.1:8545 using Web3.HTTPProvider.

Blockchain / Solidity

# Import Web3 and create w3 connection to 'http://127.0.0.1:8545'
# Your code here

Need a hint?

Use Web3.HTTPProvider with the URL 'http://127.0.0.1:8545' to connect.

2

Set up account with private key

Create a variable private_key with the exact string '0x4c0883a69102937d6231471b5dbb6204fe512961708279a1a3e7e7a7a4e9f7a3'. Then create an account variable by calling w3.eth.account.from_key(private_key).

Blockchain / Solidity

from web3 import Web3

w3 = Web3(Web3.HTTPProvider('http://127.0.0.1:8545'))

# Create private_key and account variables
# Your code here

Need a hint?

Use the exact private key string and w3.eth.account.from_key to create the account.

3

Check account balance and prepare transaction

Get the balance of account.address using w3.eth.get_balance(account.address) and store it in balance. Then create a tx dictionary with keys: to set to '0x000000000000000000000000000000000000dead', value set to w3.to_wei(0.01, 'ether'), gas set to 21000, and gasPrice set to w3.to_wei(50, 'gwei'). Also add nonce with w3.eth.get_transaction_count(account.address).

Blockchain / Solidity

from web3 import Web3

w3 = Web3(Web3.HTTPProvider('http://127.0.0.1:8545'))

private_key = '0x4c0883a69102937d6231471b5dbb6204fe512961708279a1a3e7e7a7a4e9f7a3'
account = w3.eth.account.from_key(private_key)

# Get balance and create tx dictionary
# Your code here

Need a hint?

Use w3.eth.get_balance and build the transaction dictionary with the exact keys and values.

4

Sign and print transaction hash

Sign the transaction tx with account.sign_transaction(tx) and store it in signed_tx. Then print the transaction hash as a hex string using print(signed_tx.hash.hex()).

Blockchain / Solidity

from web3 import Web3

w3 = Web3(Web3.HTTPProvider('http://127.0.0.1:8545'))

private_key = '0x4c0883a69102937d6231471b5dbb6204fe512961708279a1a3e7e7a7a4e9f7a3'
account = w3.eth.account.from_key(private_key)

balance = w3.eth.get_balance(account.address)
tx = {
    'to': '0x000000000000000000000000000000000000dead',
    'value': w3.to_wei(0.01, 'ether'),
    'gas': 21000,
    'gasPrice': w3.to_wei(50, 'gwei'),
    'nonce': w3.eth.get_transaction_count(account.address)
}

# Sign the transaction and print the transaction hash
# Your code here

Need a hint?

Use account.sign_transaction(tx) and print the hex string of the hash with .hash.hex().