Why JEST does not work with import statement / NEXTJS?

Question

I'm new to unit test in JavaScript, and I'm trying to write a unit test to a Next JS project, but I got this error in response:

Code:

    import {isBase64} from '../../service/base64-service'

test('should return false for a invalid base64 string', () => {
        expect(
            isBase64('YWJj')
        )
            .toBe(false);
    }
)

Error:

● 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

Answer 1

I found out what I needed to do, the answer was on the documentation 😅:

#1: add this dependence:

yarn add --dev  @babel/plugin-transform-modules-commonjs

#2: Edit the .babelrc file: if you don't have it, create it at the root folder

{
  "presets": ["next/babel"],
  "env": {
    "test": {
      "plugins": ["@babel/plugin-transform-modules-commonjs"]
    }
  },
  "plugins": []
}

And now your unit test is going to work with import statements as well 🥰