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Alexandru Bereghici
Alexandru Bereghici

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How to test your GitHub Pull Requests with CodeSandbox CI

This article was originally posted here

If you're an open source project maintainer or you plan to create one, you should consider using CodeSandbox CI in your project configuration. CodeSandbox CI it's an awesome GitHub application that auto-builds your open source project from pull requests. This can save a lot of time and effort to test and approve the changes.

How does it work?

Whenever someone opens a new pull request, CodeSandbox CI builds a new version of your project. Those builds get posted to CodeSandbox registry, so you can test it in there or locally, and all without having to publish the build to npm⁠.

How do I set this up?

Let's create a demo project to see CodeSandbox CI in action. For that, create a new project on GitHub and name it, for example, codesandbox-ci-test. Clone it locally and add a package.json file with the following content:

  "name": "codesandbox-ci-test",
  "version": "1.0.0",
  "main": "dist/index.js",
  "engines": {
    "node": ">=12"
  "scripts": {
    "build": "kcd-scripts build"
  "peerDependencies": {
    "react": "^17.0.2"
  "devDependencies": {
    "kcd-scripts": "^11.2.2",
    "react": "^17.0.2"
  "dependencies": {
    "@babel/runtime": "^7.16.0"
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This is a standard package.json file for a JavaScript project. We'll be using kcd-scripts to build our project, and we'll be using react to create a small reusable component for this demo. @babel/runtime is required by kcd-scripts, otherwise it won't build the project.

In src/index.js create a simple Counter component:

import * as React from 'react';

export default function Counter() {
  const [count, setCount] = React.useState(0);

  return (
      <p>You clicked {count} times!!!</p>
      <button onClick={() => setCount(count + 1)}>Click me</button>
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Install the CodeSandbox Github application from in our new repository.

Create a file called ci.json in a folder called .codesandbox in the root of the repository and add:

  "buildCommand": "build",
  "node": "12",
  "sandboxes": ["/cra-template"]
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  • buildCommand indicates which script in package.json should run to build the project.
  • node is the Node.js version to use for building the PR.
  • sandboxes is the list of sandboxes that we want to be generated. The default value is vanilla.

We don't want to use a default sandbox, because we'll have to modify manually the sandbox code to import and display the Counter component. Instead, we'll create a custom template, named cra-template.

Create a new folder named cra-template, inside of this folder create a package.json:

  "name": "react-starter-example",
  "version": "1.0.0",
  "description": "React example starter project",
  "main": "src/index.js",
  "dependencies": {
    "react": "17.0.2",
    "react-dom": "17.0.2",
    "react-scripts": "4.0.0"
  "devDependencies": {
    "@babel/runtime": "7.13.8",
    "typescript": "4.1.3"
  "scripts": {
    "start": "react-scripts start",
    "build": "react-scripts build",
    "test": "react-scripts test --env=jsdom",
    "eject": "react-scripts eject"
  "browserslist": [">0.2%", "not dead", "not ie <= 11", "not op_mini all"]
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Create a src folder and a index.js file with:

import { StrictMode } from 'react';
import ReactDOM from 'react-dom';
import Counter from 'codesandbox-ci-test';

const rootElement = document.getElementById('root');
    <Counter />
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Create a public folder with a index.html file with:

<!DOCTYPE html>
<html lang="en">
    <meta charset="utf-8" />
      content="width=device-width, initial-scale=1, shrink-to-fit=no"
    <meta name="theme-color" content="#000000" />
    <link rel="manifest" href="%PUBLIC_URL%/manifest.json" />
    <link rel="shortcut icon" href="%PUBLIC_URL%/favicon.ico" />
    <title>React App</title>
    <noscript> You need to enable JavaScript to run this app. </noscript>
    <div id="root"></div>
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At this point we can create a new pull request and see our configuration in action. The CodeSandbox CI app will build the project and will leave a comment on the pull request.

CodeSandbox comment on pull request

You can checkout the following links to see the result:

CodeSandbox CI dashboard for PRs:

CodeSandbox app:

Useful Links & Documentation

If you encountered any issues along the way, please check the Github repository with the code from this article.

If you're interested in using CodeSandbox CI in a mono-repo project, you can check out the Design System project from Twilio to see their configuration.

For more information about CodeSandbox CI, check out the documentation.

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