UPDATED: May 23, 2022
We can use this quick way to do it. Read more here: https://ethereum-waffle.readthedocs.io/en/latest/matchers.html
expect(() => contract.connect(owner).withdrawAllETH())
.to.changeEtherBalance(owner, parseEther(10));
Let's say you are implementing the NFT selling contract. And the owner can withdraw the ETH to herself.
Something like this.
// solidity
function withdrawAllETH() onlyOwner {
uint256 balance = address(this).balance;
Address.sendValue(payable(owner()), balance);
}
What do we want to test? 🧑🔧
One of them is to check if the owner receive the ETH correctly! 🤑
Let's do it together! 🔥
Note: I am using Hardhat here as a sample of testing.
// javascript
it('owner can withdraw all ETH', async () => {
// let's say contract has 5 ETH, owner has 10 ETH
// 1. let's do a withdrawal
await contract.connect(owner).withdrawAllETH()
// 2. Now owner should have 15 ETH, right?
expect(await owner.getBalance()).to.eq(parseEther(15))
})
And when we run it.
❌ AssertionError: Expected "14999957824852287212" to be equal 15000000000000000000
What the bug!? 🐞🐞🐞
The test says the actual balance is 14.999.. ETH not 15 ETH. Well... I forgot to check about the gas spent. But how do we do it?
Thanks to our beloved StackOverflow thread (as always 😂), we got a solution.
Gas Spent = Gas Used x Effective Gas Price
And we can get the data from the transaction receipt!
Note: we can use
cumulativeGasUsedinstead ofgasUsedif you want to get the gas spent from the whole block.
The Solution 🌟
Ok, now I know it, let's do this instead.
// 2nd attempt
it('owner can withdraw all ETH', async () => {
// let's say contract has 5 ETH, owner has 10 ETH
// 1. let's do a withdrawal
const tx = await contract.connect(owner).withdrawAllETH()
// 2. Let's calculate the gas spent
const receipt = await tx.wait()
const gasSpent = receipt.gasUsed.mul(receipt.effectiveGasPrice)
// 3. Now we know, it is 15 ETH minus by gasSpent!
expect(await owner.getBalance()).to.eq(parseEther(15).sub(gasSpent))
})
And when we run it.
✔ owner can withdraw all ETH
Yey! And now it works! 🥳🥳🥳
Top comments (1)
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