---
myst:
html_meta:
"description": "Test JavaScript and TypeScript scripts in Remix IDE using the Chai assertion library and Mocha test framework."
"keywords": "chai mocha remix, JavaScript testing, remix ide, mocha tests, chai assertions"
---
# Testing using Chai & Mocha
_(Supported since Remix IDE v0.22.0)_
Remix supports testing of your files in JavaScript using assertion library [Chai](https://www.chaijs.com/) & test framework [Mocha](https://mochajs.org/)
_Chai is a BDD / TDD assertion library for node and the browser that can be delightfully paired with any JavaScript testing framework._
_Mocha is a feature-rich JavaScript test framework running on Node.js and in the browser, making asynchronous testing simple and fun._
## Write tests
Create a js file in your project workspace. Better to create it inside `scripts` folder. Let's name it `sample.test.js`.
Write your tests in the file. Here is a sample:
```JavaScript
const { expect } = require("chai");
describe("Sample", function () {
it("Sample tests with mocha and chai", async function () {
var foo = 'bar'
var beverages = { tea: [ 'chai', 'matcha', 'oolong' ] };
expect(foo).to.be.a('string');
expect(foo).to.equal('bar');
expect(foo).to.have.lengthOf(3);
expect(beverages).to.have.property('tea').with.lengthOf(3);
});
});
```
## Run tests
Once done with writing the tests, right click on file name in `File Explorers` plugin. It will show some options along with option to `Run`. This `Run` option is used to run the JavaScript scripts.
Click on `Run`, tests will be executed and result will be shown on Terminal.
## Test a contract
Similarly unit tests can be written to test the functionality of a smart contract. An example to test default `1_Storage.sol` contract can be as:
```JavaScript
const { expect } = require("chai");
describe("Storage", function () {
it("test initial value", async function () {
// Make sure contract is compiled and artifacts are generated
const metadata = JSON.parse(await remix.call('fileManager', 'getFile', 'contracts/artifacts/Storage.json'))
const signer = (new ethers.providers.Web3Provider(web3Provider)).getSigner()
let Storage = new ethers.ContractFactory(metadata.abi, metadata.data.bytecode.object, signer);
let storage = await Storage.deploy();
console.log('storage contract Address: ' + storage.address);
await storage.deployed()
expect((await storage.retrieve()).toNumber()).to.equal(0);
});
it("test updating and retrieving updated value", async function () {
const metadata = JSON.parse(await remix.call('fileManager', 'getFile', 'contracts/artifacts/Storage.json'))
const signer = (new ethers.providers.Web3Provider(web3Provider)).getSigner()
let Storage = new ethers.ContractFactory(metadata.abi, metadata.data.bytecode.object, signer);
let storage = await Storage.deploy();
await storage.deployed()
const setValue = await storage.store(56);
await setValue.wait();
expect((await storage.retrieve()).toNumber()).to.equal(56);
});
it("fail test updating and retrieving updated value", async function () {
const metadata = JSON.parse(await remix.call('fileManager', 'getFile', 'contracts/artifacts/Storage.json'))
const signer = (new ethers.providers.Web3Provider(web3Provider)).getSigner()
let Storage = new ethers.ContractFactory(metadata.abi, metadata.data.bytecode.object, signer);
let storage = await Storage.deploy();
await storage.deployed()
const setValue = await storage.store(56);
await setValue.wait();
expect((await storage.retrieve()).toNumber()).to.equal(55);
});
});
```
Result will be as:
## Debugging a test transaction
To debug a transaction in one of the tests, print the transaction hash and input that in the [Remix Debugger plugin](https://remix-ide.readthedocs.io/en/latest/tutorial_debug.html).
## Hardhat-ethers support
Remix also supports methods of [hardhat-ethers](https://hardhat.org/hardhat-runner/plugins/nomicfoundation-hardhat-ethers) plugin of Hardhat framework. Available methods under this plugin are:
```TypeScript
interface Libraries {
[libraryName: string]: string;
}
interface FactoryOptions {
signer?: ethers.Signer;
libraries?: Libraries;
}
function getContractFactory(name: string, signer?: ethers.Signer): Promise;
function getContractFactory(name: string, factoryOptions: FactoryOptions): Promise;
function getContractFactory(abi: any[], bytecode: ethers.utils.BytesLike, signer?: ethers.Signer): Promise;
function getContractAt(name: string, address: string, signer?: ethers.Signer): Promise;
function getContractAt(abi: any[], address: string, signer?: ethers.Signer): Promise;
function getSigners() => Promise;
function getSigner(address: string) => Promise;
function getContractFactoryFromArtifact(artifact: Artifact, signer?: ethers.Signer): Promise;
function getContractFactoryFromArtifact(artifact: Artifact, factoryOptions: FactoryOptions): Promise;
function getContractAtFromArtifact(artifact: Artifact, address: string, signer?: ethers.Signer): Promise;
```
With this, one can run the tests for a hardhat project easily using Remix.
Example to test `Storage` contract with this plugin methods can be as:
```JavaScript
const { expect } = require("chai");
const { ethers } = require("hardhat");
describe("Storage", function () {
it("test initial value", async function () {
const Storage = await ethers.getContractFactory("Storage");
const storage = await Storage.deploy();
await storage.deployed();
console.log('storage deployed at:'+ storage.address)
expect((await storage.retrieve()).toNumber()).to.equal(0);
});
it("test updating and retrieving updated value", async function () {
const Storage = await ethers.getContractFactory("Storage");
const storage = await Storage.deploy();
await storage.deployed();
const storage2 = await ethers.getContractAt("Storage", storage.address);
const setValue = await storage2.store(56);
await setValue.wait();
expect((await storage2.retrieve()).toNumber()).to.equal(56);
});
});
```
Result will be as:
