Ethereum TestNets Overview
Since its creation ethereum has been mined through a so-called proof-of-work model, It involves complex math equations that massive numbers of machines race to solve, and also it requires an abundance of energy.
Rather than relying on energy-intensive mining, the new method POS requires users to leverage their existing cache of ether as a means to verify transactions and mint tokens. It uses far less power and is expected to translate into faster transactions
The upgrade from the original proof-of-work mechanism to proof-of-stake was called The Merge, Merge is Ethereum's long-awaited move to becoming a proof-of-stake blockchain, under which the current proof-of-work chain will merge with the new proof-of-stake one.
The Merge refers to the original Ethereum Mainnet merging with a separate proof-of-stake blockchain called the Beacon Chain
It's a big change and there have been multiple test networks to see whether it will work and ensure that the new proof-of-stake protocol runs smoothly , simulate a process identical to what the main network, or mainnet will execute , And these Testnets allow developers to try out new things and make necessary tweaks before the updates roll out across the main blockchain.
The below are the three Ethereum merge Testnets
Seploia - https://sepolia.dev/
Ropsten - https://fauceth.komputing.org/
Goerli - https://goerli.net/
All this names are based on names of trains and metro stations of the world.
Ropsten a metrostation in Stockholm Seploia is a city Athens Goerli is located in Berlin
These test networks used by protocol developers , smart contract developers to test both protocol upgrades as well as smart contracts in a production-like environment and to test Dapp’s will be able to work properly in the POS system.
Sepolia – Sepolia is the first Ethereum Testnet and first of its kind on any of the Ethereum proof-of-stake testnet
Ropsten - Ropsten a metrostation in Stockholm
Goerli -- (named for a train station in Berlin) Goerli was the last of three public testnets to run through before the Merge.
Finally the mainnet Merge occured on 15thSeptember 2022 which completed Ethereum's transition to proof-of-stake consensus
After this merge the old Testnet Rinkeby, Ropsten , Kovan Testnet are deprecated and will no longer receive protocol upgrades.