The testnet ran from August 2019 to January 2022. Some incompatible tests were performed, which required special rules in the program code. A testnet should also be as close as possible to the mainnet. For the switch to deterministic masternodes in 2022, a clean testnet is useful before the productive mainnet follows.
On January 8, testnet4 was launched and the previous testnet3 was archived. Both blockchains can be accessed with the Explorer on