_Follow along with this video:_ --- ### Solving the Anvil problem When we needed the Sepolia `priceFeed` we made sure that our deployments script pointed to it. How can we solve this in Anvil, because the contract that we need doesn't exist there. Simple, we deploy mocks. Our `getAnvilEthConfig` function in `HelperConfig` must deploy a mock contract. After it deploys it we need it to return the mock address, so our contracts would know where to send their calls. First of all, we need to make sure we import `Script.sol` in the `HelperConfig.s.sol` contract. Also, `HelperConfig` needs to inherit from `Script`. This will give us access to the `vm.startBroadcast`/`vm.stopBroadcast` functionality. We will use this to deploy our mocks. But ... what is a mock contract? **A mock contract is a special type of contract designed to simulate the behavior of another contract during testing.** Update your start of the `HelperConfig.s.sol` file as follows: ```solidity import {Script} from "forge-std/Script.sol"; contract HelperConfig is Script { } ``` In order to be able to deploy a mock contract we need ... a mock contract. So, in `test` folder please create a new folder called `mocks`. Inside `mocks` create a new file `MockV3Aggregator.sol`. Rewriting the AggregatorV3 as a mock is not the easiest task out there. Please copy the contents of [this contract](https://github.com/Cyfrin/foundry-fund-me-f23/blob/main/test/mock/MockV3Aggregator.sol) into your newly created file. What next? We need to import this in our `HelperConfig.s.sol` file and deploy it in the `getAnvilEthConfig` then return the address. Perform the following changes in `HelperConfig`: ```solidity import {MockV3Aggregator} from "../test/mocks/MockV3Aggregator.sol"; [...] // In state variables section MockV3Aggregator mockPriceFeed; [...] function getAnvilEthConfig() public returns (NetworkConfig memory) { vm.startBroadcast(); mockPriceFeed = new MockV3Aggregator(8, 2000e8); vm.stopBroadcast(); NetworkConfig memory anvilConfig = NetworkConfig({ priceFeed: address(mockPriceFeed) }); return anvilConfig; } ``` More testing and refactorings in the next lessons!