Module 4: Using Regtest to Simulate Bitcoin

Learning Objectives

By the end of this module, you will:

Understand the purpose and power of Bitcoin Core's regtest mode

Set up a private, fully controlled Bitcoin network

Mine blocks and confirm transactions instantly

Use regtest for API testing, integration flows, and simulations

Why Regtest Matters

regtest stands for Regression Test mode. It is a fully offline, developer-first Bitcoin network that:

Has no network peers (your node is the entire network)

Lets you mine blocks instantly

Offers zero-fee, instant transaction confirmation

Works perfectly with automated testing, CI flows, and local wallets

For building real Bitcoin apps, is the the fastest and safest sandbox.

Setting Up a Fully Isolated Bitcoin Environment

Start your node in regtest mode:

Start bitcoind in regtest

This creates:

~/.bitcoin/regtest/ as your data directory

A zero-block chain, ready to mine

No connections to testnet, mainnet, or the internet

You can confirm the mode using:

Confirm regtest mode

Look for "chain": "regtest"

Mining Blocks Instantly

Regtest allows manual block generation.

First, create a wallet and get a new address:

Create wallet and get address for mining

Now mine 101 blocks (to unlock coinbase rewards):

Generate Blocks in Regtest Mode

This gives you spendable BTC for testing.

You can generate 1 block at a time to simulate confirmation behavior.

Sending Transactions Instantly

With freshly mined coins, you can now send BTC:

Send BTC and check mempool

Check mempool:

Check mempool

Confirm instantly by mining a block:

Mine a block to confirm

Now check the recipient’s balance:

Check balance

GUI Alternative: Polar

Polar is a desktop app that sets up a regtest Bitcoin + Lightning network for you using Docker.

Why use it?

No terminal needed

Visual interface for nodes, wallets, payments

Supports Bitcoin Core + LND + Core Lightning

🖥️ If you prefer a GUI for testing, Polar is highly recommended. It is especially useful for team demos, education, and debugging.

Install it via:

macOS: brew install --cask polar

Linux: .AppImage from GitHub

Windows: .exe installer

You can still inspect logs, addresses, and transactions under the hood.

Activity

Set up a regtest sandbox from scratch:

Start bitcoind in regtest mode.

Create a wallet, generate 101 blocks (replace <your_address> with an address from the new wallet).

Send 2 test transactions (replace <destination_1>, <destination_2> with valid addresses).

Mine 1 block to confirm (use the same <your_address> as before or another address in activity_wallet).

Use listtransactions to view history.

Wallets that understand UTXOs deeply will control fees, preserve privacy, and scale cleanly over time.

Bonus:

Try doing the same flow inside Polar