Migrate metatx tests to ethers.js (#4737)

Co-authored-by: ernestognw <ernestognw@gmail.com>

test/helpers/account.js

@@ -4,10 +4,10 @@ const { impersonateAccount, setBalance } = require('@nomicfoundation/hardhat-net
 // Hardhat default balance
 const DEFAULT_BALANCE = 10000n * ethers.WeiPerEther;
 
-async function impersonate(account, balance = DEFAULT_BALANCE) {
-  await impersonateAccount(account);
-  await setBalance(account, balance);
-}
+const impersonate = (account, balance = DEFAULT_BALANCE) =>
+  impersonateAccount(account)
+    .then(() => setBalance(account, balance))
+    .then(() => ethers.getSigner(account));
 
 module.exports = {
   impersonate,

test/helpers/math.js

@@ -1,6 +1,7 @@
 module.exports = {
   // sum of integer / bignumber
   sum: (...args) => args.reduce((acc, n) => acc + n, 0),
+  bigintSum: (...args) => args.reduce((acc, n) => acc + n, 0n),
   BNsum: (...args) => args.reduce((acc, n) => acc.add(n), web3.utils.toBN(0)),
   // min of integer / bignumber
   min: (...args) => args.slice(1).reduce((x, y) => (x < y ? x : y), args[0]),