Blockchain testnets play an essential role in the ecosystem, offering developers a sandbox-like environment to experiment, debug, and validate their blockchain projects and smart contracts safely before going live on the mainnet.
This article explores what blockchain testnets are, their importance in protocols and smart contract development, and the different types of Ethereum testnets that exist.
A blockchain testnet, or test network, is an alternative blockchain used specifically for testing and development purposes. It is often nearly a replica of the main blockchain environment and architecture, known as the mainnet, where the actual transactions occur and real crypto assets have value. However, the crucial difference is that the assets on a testnet are purely for testing; they have no real-world value.
This distinction allows developers to experiment without the risk of financial loss or affecting the main blockchain.
There are several reasons they don’t have real value:
However, we have seen history where a testnet eventually becomes valuable, for example, when Goerli was worth money. Goerli became worth money when many people wanted to deploy smart contracts to test, but it was too hard to get ETH for testing! So, some people started paying for Goerli ETH.
For the most part, testnets are public goods meant to aid developers looking to test and tinker with smart contract applications. Of course, if you’re following the Solidity smart contract development courses Cyfrin Updraft, you should always test locally before even thinking about going for a testnet!
Here’s a list of currently active and deprecated blockchain testnets you should know about:
People often use testnets to give protocol users a chance to play with the protocol in a simulated environment. Additionally, testnets are a good way to test whether an application works with third-party tools, like block explorers (e.g., Etherscan), token URIs (e.g., For NFTs), and more.
A crypto faucet is a tool available for many blockchain testnets that dispenses a small amount of native cryptocurrency.
Developers use testnet faucets to obtain testnet funds to deploy, test, and interact with a smart contract or protocol on a blockchain testnet.
As of writing, the most popular EVM testnet is Ethereum Sepolia. To interact with this testnet, you can grab some test ETH from any of the following faucets:
Note: As we mentioned, testnets are designed to be deprecated eventually, and deprecation usually happens every couple of years. Because of this, faucets and popular testnets often stop working.
Visit the foundry curriculum to see the testnet and faucets that Cyfrin Updraft currently recommends.
Most blockchain testnets eventually shut down to ensure they never have value. People running testnet blockchain nodes are aware of this and often run a testnet node to help new developers work on a sandbox environment for them to test.
Testnets are blockchains that mirror mainnet blockchains, except their purpose is to be a testing and sandbox environment with no real value. Testnets are considered “public goods” because the people running them stand to gain nothing or almost nothing from them.
