Vite / Jest / React-Testing

Question

I am trying to test in React application with Jest; my application uses Vite as a module bundler. The issue is, every time I run tests I get the following error:

   > [email protected] test
> jest

 FAIL  src/test/App.test.jsx
  ● Test suite failed to run

    Jest encountered an unexpected token

    Jest failed to parse a file. This happens e.g. when your code or its dependencies use non-standard JavaScript syntax, or when Jest is not configured to support such syntax.

    Out of the box Jest supports Babel, which will be used to transform your files into valid JS based on your Babel configuration.

    By default "node_modules" folder is ignored by transformers.

    Here's what you can do:
     • If you are trying to use ECMAScript Modules, see https://jestjs.io/docs/ecmascript-modules for how to 
enable it.
     • If you are trying to use TypeScript, see https://jestjs.io/docs/getting-started#using-typescript      
     • To have some of your "node_modules" files transformed, you can specify a custom "transformIgnorePatterns" in your config.
     • If you need a custom transformation specify a "transform" option in your config.
     • If you simply want to mock your non-JS modules (e.g. binary assets) you can stub them out with the "moduleNameMapper" config option.

    You'll find more details and examples of these config options in the docs:
    https://jestjs.io/docs/configuration
    For information about custom transformations, see:
    https://jestjs.io/docs/code-transformation

    Details:

    SyntaxError: C:\Users\Tomas\Desktop\react-test\src\test\App.test.jsx: Support for the experimental syntax 'jsx' isn't currently enabled (8:30):

       6 |
       7 | test("renders content", ()=>{
    >  8 |     const component = render(<App></App>)
         |                              ^
       9 |     console.log(component)
      10 | })

    Add @babel/preset-react (https://git.io/JfeDR) to the 'presets' section of your Babel config to enable transformation.
    If you want to leave it as-is, add @babel/plugin-syntax-jsx (https://git.io/vb4yA) to the 'plugins' section to enable parsing.

      at Parser._raise (node_modules/@babel/parser/src/parser/error.js:150:45)
      at Parser.raiseWithData (node_modules/@babel/parser/src/parser/error.js:145:17)
      at Parser.expectOnePlugin (node_modules/@babel/parser/src/parser/util.js:214:18)
      at Parser.parseExprAtom (node_modules/@babel/parser/src/parser/expression.js:1238:16)
      at Parser.parseExprSubscripts (node_modules/@babel/parser/src/parser/expression.js:682:23)
      at Parser.parseUpdate (node_modules/@babel/parser/src/parser/expression.js:662:21)
      at Parser.parseMaybeUnary (node_modules/@babel/parser/src/parser/expression.js:633:23)
      at Parser.parseMaybeUnaryOrPrivate (node_modules/@babel/parser/src/parser/expression.js:388:14)        
      at Parser.parseExprOps (node_modules/@babel/parser/src/parser/expression.js:398:23)
      at Parser.parseMaybeConditional (node_modules/@babel/parser/src/parser/expression.js:356:23)

Test Suites: 1 failed, 1 total
Tests:       0 total
Snapshots:   0 total
Time:        1.379 s
Ran all test suites.

Package.json

{
  "name": "react-test",
  "private": true,
  "version": "0.0.0",
  "type": "module",
  "scripts": {
    "dev": "vite",
    "build": "vite build",
    "preview": "vite preview",
    "test": "jest"
  },
  "dependencies": {
    "react": "^17.0.2",
    "react-dom": "^17.0.2"
  },
  "jest": {
    "verbose": true,
    "testEnvironment": "jsdom",
    "transform": {
      "^.+\\.(js|jsx)$": "babel-jest"
    },
    "moduleFileExtensions": [
      "js",
      "jsx"
    ],
    "moduleNameMapper": {
      "\\.(gif|ttf|eot|svg|png)$": "<rootDir>/test/__mocks__/fileMock.js",
      "\\.(css|less|sass|scss)$": "identity-obj-proxy"
    }
  },
  "devDependencies": {
    "@babel/plugin-syntax-jsx": "^7.16.7",
    "@testing-library/jest-dom": "^5.16.2",
    "@testing-library/react": "^12.1.3",
    "@types/jest": "^27.4.1",
    "@vitejs/plugin-react": "^1.0.7",
    "jest": "^27.5.1",
    "vite": "^2.8.0"
  }
}

App.test.jsx

import React from "react";
import "@testing-library/jest-dom/extend-expect"
import { render } from "@testing-library/react";
import App from "../App.jsx";


test("renders content", ()=>{
    const component = render(<App></App>)
    console.log(component)
})

Answer 1

The error output is correct, Jest runs on your local node binary and requires that your jsx files be transformed into a syntax it can understand.

Vite does not so this transformation by default. It was designed to transpile and bundle your code into some bundle.js that is appropriate for the browser (it can do other types of output, like libraries. You'd need to tweak your vite.config.js).

Luckily, other folks have solved this problem for you. I'd recommend using vitest, since you wouldn't need to download another transformer or invest a lot of time into setting up tricky build scripts.

Here's a guide on how to quickly set it up:

https://www.eternaldev.com/blog/testing-a-react-application-with-vitest/

And a migration guide:

https://vitest.dev/guide/migration.html