What is the name of the Bitcoin network's test environment?

The Bitcoin network’s test environment is called Testnet.

Testnet is a separate public blockchain designed for developers, wallet authors, node operators, and testers. It follows Bitcoin-like rules but uses separate coins that are not supposed to have monetary value. This lets people test transactions, fee handling, wallet recovery, and software upgrades without risking real bitcoin on mainnet.

Testnet is not simply a private copy of mainnet. It has its own genesis block, peer-discovery infrastructure, address version, and network ports. For example, traditional testnet addresses use different version data so that test coins cannot accidentally be sent as mainnet bitcoin. Bitcoin Core can be run in testnet mode with the “-testnet” option.

Signet and Regtest are common mix-ups because they are also testing environments. Signet uses signed blocks and is intended to be more predictable, while Regtest creates a local blockchain useful for controlled automated tests. Mainnet is the production network where real BTC has value. In ordinary Bitcoin terminology, however, “the test environment” refers to Testnet.