How do I retrieve the exact gas costs spent for a transaction with ethers.js?

Question

Running

      const receipt = await contract.mint(4)
      console.log(receipt)

gives me the following transaction receipt

{
  hash: '0xee7c081488965518d3cb8d23a13a4eabf728a6f1842c9b1249679a8b809bcf29',
  type: 2,
  accessList: [],
  blockHash: '0x741edbbc20aa711b80cbcbf6f7cf4ffed88bc042a4417ddbeb0b38d7fdf385cc',
  blockNumber: 3,
  transactionIndex: 0,
  confirmations: 1,
  from: '0x70997970C51812dc3A010C7d01b50e0d17dc79C8',
  gasPrice: BigNumber { _hex: '0x65013202', _isBigNumber: true },
  maxPriorityFeePerGas: BigNumber { _hex: '0x3b9aca00', _isBigNumber: true },
  maxFeePerGas: BigNumber { _hex: '0x8e679a04', _isBigNumber: true },
  gasLimit: BigNumber { _hex: '0x01bad518', _isBigNumber: true },
  to: '0x5FbDB2315678afecb367f032d93F642f64180aa3',
  value: BigNumber { _hex: '0x00', _isBigNumber: true },
  nonce: 0,
  data: '0xfe234aac0000000000000000000000000000000000000000000000000000000000000004',
  r: '0xc0edd7dc1a026cddeee860ab6f7d1aacf80a0c3c9ef3a119a49382662a74f39d',
  s: '0x3b1a06a0df530e153bd22852d5956e59dbcac0250eda1cdd961e71554027f60e',
  v: 1,
  creates: null,
  chainId: 31337,
  wait: [Function (anonymous)]
}

I want to run tests with waffle and would like to make sure that the refund is implemented correctly. For that I want to see if the account balance difference equals the transaction value minus the refund. The problem is that I now have to take gas costs into account. How do I accurately factor these out?

Answer 1

After a bit of searching I figured out that the receipt should be the mined object.. I also wasn't sending any value with the transaction.

      const addr1Bal = await provider.getBalance(addr1.address)
      const txValue = ethers.utils.parseEther('0.03').mul(BigNumber.from('4'))
      const tx = await contract.connect(addr1).mint(4, { value: txValue })
      const receipt = await tx.wait()
      console.log('total ether spent on gas for transaction: \t', ethers.utils.formatEther(receipt.gasUsed.mul(receipt.effectiveGasPrice)))
      console.log('balance difference minus transaction value: \t', ethers.utils.formatEther(addr1Bal.sub(await provider.getBalance(addr1.address)).sub(txValue)))

prints

total ether spent on gas for transaction:        0.000768148434753892
balance difference minus transaction value:      0.000768148434753892