How to get a specific number of signers while testing smart contracts in Hardhat?

I am developing my smart contracts in Hardhat and testing on RSK Testnet. To create signer accounts, I am using a mnemonic seed phrase and the following Hardhat configuration:

require('@nomicfoundation/hardhat-toolbox');
const { mnemonic } = require('./.secret.json');

/** @type import('hardhat/config').HardhatUserConfig */
module.exports = {
  solidity: '0.8.16',
  networks: {
    hardhat: {},
    rsktestnet: {
      chainId: 31,
      url: 'https://public-node.testnet.rsk.co/',
      accounts: { // <-- here
        mnemonic,
        path: "m/44'/60'/0'/0",
      },
    },
  },
  // ...
};

In my tests, I usually use an ethers.js helper function to get an array of signers in my tests:

const signers = await hre.ethers.getSigners();

However this function returns 20 signer wallets. Is there a way to get a specific amount of wallets, if I don't want this default amount?

Solution

You can use the Wallet.fromMnemonic function from ethers.js to do this.

Within hardhat.config.js, or anywhere where you import the hre variable, you can do so by invoking it like so: hre.ethers.Wallet.fromMnemonic(mnemonic, derivationPath?, wordList?)

This function is used to generate a single wallet. The function's second argument is the BIP-32 derivation path. Since the one that you are using in config is m/44'/60'/0'/0, then by default the function will append /0, resulting in m/44'/60'/0'/0/0 to generate the 1st wallet.

If you want to generate another one, you could specify m/44'/60'/0'/0/1 (with /1 appended).

To generate a specific number of wallets, simply do the above in a loop, changing the final index in the derivation path in each iteration.

For example, the following function will obtain 10:

function getSigners(amount = 40) {
  // getting seed phrase and derivation path from the hardhat config
  const { mnemonic, path } = hre.network.config.accounts
  return [...Array(amount).keys()].map((i) =>
    hre.ethers.Wallet.fromMnemonic(mnemonic, `${path}/${i}`)
      .connect(hre.ethers.provider),
  )
}