#Hardhat Chai Matchers
This plugin adds Ethereum-specific capabilities to the Chai assertion library, making your smart contract tests easy to write and read.
Check its documentation to learn more.
#Installation
We recommend using npm 7 or later. If you do that, then you just need to install the plugin itself:
npm install --save-dev @nomicfoundation/hardhat-chai-matchers
If you are using an older version of npm, you'll also need to install all the packages used by the plugin.
npm install --save-dev @nomicfoundation/hardhat-chai-matchers chai@4 @nomicfoundation/hardhat-ethers ethers
That's also the case if you are using yarn:
yarn add --dev @nomicfoundation/hardhat-chai-matchers chai@4 @nomicfoundation/hardhat-ethers ethers
#Usage
After installing it, add the plugin to your Hardhat config:
require("@nomicfoundation/hardhat-chai-matchers");
Then you'll be able to use the matchers in your tests:
expect(await token.totalSupply()).to.equal(1_000_000);
await expect(token.transfer(token, 1000)).to.be.revertedWith(
"Cannot transfer to the contract itself"
);
await expect(token.transfer(recipient, 1000))
.to.emit(token, "Transfer")
.withArgs(owner, recipient, 1000);
#Known issues
#Chaining Async Matchers
Currently, the following matchers do not support chaining:
reverted
revertedWith
revertedWithCustomError
revertedWithoutReason
revertedWithPanic
changeEtherBalance
changeEtherBalances
changeTokenBalance
changeTokenBalances
emit
(with the only exception of chaining multipleemit
matchers)
Which means you can't do:
await expect(contract.f(...))
.to.changeEtherBalance(...)
.and.to.changeTokenBalance(...)
To work around this limitation, write separate assertions for each matcher:
const tx = contract.f(...);
await expect(tx).to.changeEtherBalance(...)
await expect(tx).to.changeTokenBalance(...)
If you are interested in seeing an implementation of chaining for async matchers, please visit the GitHub issue #4235 and leave an upvote or comment.