testnet

A testnet is a separate blockchain network used for development, testing, and experimentation of applications and protocol changes without affecting the main network (mainnet). Testnet tokens are not intended to have real value on the mainnet and are typically obtainable for free via faucets. Testnets let developers simulate live operation, validate code, and identify bugs before deploying updates to the mainnet.

Public testnets accompany the mainnet in many ecosystems. They may use different consensus parameters, token economics, or network rules to mirror stress conditions or new features. Some testnets can be reset or recreated, and several environments support local or regtest modes for isolated development.

Examples include Bitcoin's testnet (and testnet3), Ethereum's Goerli and Sepolia in recent years (Ropsten and Rinkeby were phased out), and test networks in other ecosystems such as Polygon Mumbai, Solana devnet, and Avalanche Fuji. Private test networks, or regtest environments, are used for continuous integration and offline testing.

Usage involves deploying and testing smart contracts, wallets, or node software on the testnet, and using faucets to obtain testnet coins. Tests cover functionality, interoperability with other services, and upgrade scenarios. It is important to distinguish testnet funds from mainnet funds to avoid financial loss.

Limitations include differences from the mainnet in economics, performance, and security. Testnets may be deprecated when features are released on mainnet, and tokens may be cleared or require migration. Despite these caveats, testnets are a standard tool for safe, iterative development and network experimentation.