To the best of my knowledge Monero only has two forks, AEON and BipCoin
AEON was forked from Monero prior to the introduction of its testnet function although its lead developer plans to change that as part of the AEON roadmap
There is not a testnet because the work that was done to create a testnet function in Monero was after the AEON fork. We'll have one once we switch over to the newer code base.
I can find no mention of a public testnet for Bipcoin.
Are there any Monero forks or other CryptoNote coins with a public testnet or is Monero unique in that regard?