Get SEPOLIA TEST ETHER from TESTNET FAUCET without ETH balance in METAMASK account

To assert the balance of an account, try this:

let expectedBalance = web3.toBigNumber(web3.toWei(3, 'ether'));
let actualBalance = await web3.eth.getBalance(accounts[1]);

assert.deepEqual(actualBalance, expectedBalance, "Balance incorrect!");

To use accounts other than the first one you have to indicate so to HDWalletProvider. Third parameter is account index, default is 0. For example to use the fifth one:

provider: () => {
    return new HDWalletProvider(mnemonic, URL, 4);
}

If required you can indicate to load more than one account. To load the the first 5 accounts

provider: () => {
    return new HDWalletProvider(mnemonic, URL, 0, 5);
}

Truffle will use the first account returned from provider but you can change default account using from in truffle-config.js

networks: 
  develop: {
    provider: () => {...},
    from: "0x01230123...0123",
    gas: "4500000",
    gasPrice: "10000000000",
  }
}

You can also override default configuration passing new parameters when deploying

module.exports = function(deployer) {
  deployer.deploy(Migrations, {
    from: "0x444433332222....0000",
    gas: "1000000",
    gasPrice: "9000000000",
  });
};