Workings of web3.EthereumTesterProvider()?

You can find info here https://web3py.readthedocs.io/en/stable/providers.html

EthereumTesterProvider Warning

Experimental: This provider is experimental. There are still significant gaps in functionality. However it is being actively developed and supported.

classweb3.providers.eth_tester.EthereumTesterProvider(eth_tester=None) This provider integrates with the eth-tester library. The eth_tester constructor argument should be an instance of the EthereumTester or a subclass of BaseChainBackend class provided by the eth-tester library. If you would like a custom eth-tester instance to test with, see the eth-tester library documentation for details.

from web3 import Web3, EthereumTesterProvider
w3 = Web3(EthereumTesterProvider())