Forking and Mocking

FundMe.sol requires chainlink oracle contracts for price feeds on eth/usd. Currently it pulls this data from the contracts deployed on Rinkeby network, by passing the pricing contract's address into an interface (AggregatorV3Interface.sol)

• AggregatorV3Interface priceFeed = AggregatorV3Interface(0x8A753747A1Fa494EC906cE90E9f37563A8AF630e);

Testing can be done on live mainnet and testnet - but will be a slow process with mining lag and ETH fees. So we look to test in a private environment free of such constrains -> hence forking or mocking.

What if we want to do testing on our private development chain?

Problem: Chainlink contracts do not exists there.

Forking

• copy the mainnet (via Alchemy/Infura API)

• run mainnet fork in our private env

• prior contracts deployed on mainnet wil be available in our forked local env.

• can simply use mainnet address references.

Mocking

• deploy a mock contracts of the real thing in our development chain.

  • like MockV3Aggregator, where we decide ETH/USD price.

• deploy mock contracts on persistent mock network

• use dummy accounts [get_accounts -> account[0] -> dummy acc]

On brownie networks

There are 3 kinds of networks brownie connects to:

• Ethereum

• Ethereum Classic (We can ignore this)

• Development

You can see them by running brownie networks list in your terminal.

When creating a network in the Ethereum category, brownie will save the addresses of the contracts that were deployed, storing addresses in the build folder.

Ethereum
  ├─Mainnet (Infura): mainnet
  └─ganache-local: ganache (brownie will remember these)

Development
  ├─Ganache-CLI: development
  └─ganache-temp: ganache-temp (brownie won't remember these)

ganache-local therefore has persistency - at least till we close the ganacheUI.

If you'd like the desired experience to be such that brownie always redeploys, you can create your ganache network in the Development network instead, so brownie won't remember it's deployments, and will always deploy fresh.

This will mean though, that you won't be able to run any of the 2nd scripts, like brownie run scripts/price_feed_scripts/02_whatever_this_one_is.py since brownie won't remember any contracts being there.

brownie default network: development (Ganache-CLI)

brownie automatically latches onto ganacheUI if it is running, regardless of where we specify the --network flag to be.

This can cause errors, especially when you deploying to forked mainnet instances.

Always consider if ganacheUI has any business running in regards to your network deployment location.