How to Fork Mainnet for Testing

const CHAIN_IDS = {
  hardhat: 31337, // chain ID for hardhat testing
};
module.exports = {
  networks: {
    hardhat: {
      chainId: CHAIN_IDS.hardhat,
      forking: {
        // Using Alchemy
        url: `https://eth-mainnet.alchemyapi.io/v2/${ALCHEMY_KEY}`, // url to RPC node, ${ALCHEMY_KEY} - must be your API key
        // Using Infura
        // url: `https://mainnet.infura.io/v3/${INFURA_KEY}`, // ${INFURA_KEY} - must be your API key
        blockNumber: 12821000, // a specific block number with which you want to work
      },
    },
    ... // you can also add more necessary information to your config
  }
}

// Function which allows to convert any address to the signer which can sign transactions in a test
const impersonateAddress = async (address) => {
  const hre = require('hardhat');
  await hre.network.provider.request({
    method: 'hardhat_impersonateAccount',
    params: [address],
  });
  const signer = await ethers.provider.getSigner(address);
  signer.address = signer._address;
  return signer;
};
// Function to increase time in mainnet fork
async function increaseTime(value) {
  if (!ethers.BigNumber.isBigNumber(value)) {
    value = ethers.BigNumber.from(value);
  }
  await ethers.provider.send('evm_increaseTime', [value.toNumber()]);
  await ethers.provider.send('evm_mine');
}
// Construction to get any contract as an object by its interface and address in blockchain
// It is necessary to note that you must add an interface to your project
const WETH = await ethers.getContractAt('IWETH', wethAddress);