Testnets operate as a separate BSV network that has all the same functionality as the Mainnet, except coins transacted on them have no value. Testnets serve to provide a stable testing environment for applications such that developers do not have spent actual BSV coins before deploying their service to the Mainnet.
WhatsOnChain has a testnet block explorer with much of the same functionality as their Mainnet one.
Bitcoin SV Scaling Test Network (STN)
The BSV Scaling TestNet operates specifically to enable testing of larger block sizes and high sustained transaction volume. The STN was created in order to segregate network scaling testing from the “normal” testnet whose purpose is for application development. This network is necessary to achieve the massive scale that Bitcoin SV intends to achieve.