Doubt that any exchange will risk it with listing a coin that is still on testnet, qtrade was an exception
A lot of coins are being listed before mainnet. AE, THETA, IOTX, IOST, ZIL, ENIGMA, QLC - those are only few coins out of dozens that i remember to be go on mainnet while being actively traded on binance, priced 60M $ - 1,2B $. Enigma was listed on binance in 10/2017, started
testnet in 03/2019 (?) - 1.5 year with ETH placeholder.
Think that all those projects use Ethereum (not sure about all of them, but know that Aeternity and Enigma firstly listed as ERC20 tokens) for ICO and give tokens to buyers, and trading starts for ERC20 issued tokens. And here we have native coins, not ERC20 tokens.