Hi, I am developing a library to interact with smart contract. is there a dex in testnet that I can use to test?

every wallet is a smartcontract, you may interact with wallet.

I am basically developing a wallet

sorry, my bad english - every address in network is a smartcontract. open any address in explorer and if its state is 'active' - you can interact with it

my point is to interact with it on browser like metamask in Ethereum rather than using explorer

ye, ston.fi has a testnet version of the dex
https://testnet.tonscan.org/address/EQBsGx9ArADUrREB34W-ghgsCgBShvfUr4Jvlu-0KGc33Rbt

i understand. I mean you dont need "any DEX" smartcontract to test your library with, you may test your library with regular address smartcontract too

The reason I want a dex testnet is because dex may implement Ton Web Wallet provider to interact with browser smartcontract. so it is easier to test in my case. explorer like tonscan does not have it. I want to test ability to interact with smart contract by provider rather than manually calling it from explorer

got it. sorry, I thought you are making new wallet to interact with blockchain "directly"

for example, https://app.ston.fi/swap?ft=TON&fa=1 it can read wallet address, balance and call smart contract by interact with UI. I believe it use TonProvider behind the UI.

I want to develop something like that, but it is hard to do stuff on mainnet. so I wonder if there is a site like app.ston.fi but in testnet

You can use tx emulation in mainnet (for example, via Tonkeeper) in order to check the library.