How do I get jest to to work with ES6 dependencies

Question

So I have a dependency package that I am pulling into my node_modules folder. This package has a export in it like this

        ({"Object.<anonymous>":function(module,exports,require,__dirname,__filename,global,jest){export * from './client';

In order to get around this I use https://github.com/standard-things/esm. In my node loader

node -r esm index.js.

However this does not work with my tests which are using Jest.

I cant seem to figure out how to just get Jest to transform these imports for me. I have tried so many things, and the current state of my configuration files is.

// babel.config.js
// babel.config.js
module.exports = {
    presets: [['@babel/preset-env', { targets: { node: 'current' } }], '@babel/preset-typescript'],
    plugins: ['@babel/plugin-transform-modules-commonjs'],
};

const { pathsToModuleNameMapper } = require('ts-jest/utils');
const { compilerOptions } = require('./tsconfig');

module.exports = {
    preset: 'ts-jest',
    testEnvironment: 'node',
    testMatch: ['<rootDir>/tests/**/*.{ts,js}'],
    testPathIgnorePatterns: ['global.d.ts', 'utils.ts', '<rootDir>/node_modules/'], // tried with and without this
    moduleNameMapper: pathsToModuleNameMapper(compilerOptions.paths, { prefix: '<rootDir>/' }),
};

Still keep getting that error. Anyone have a suggestion.

Answer 1

transformIgnorePatterns defaults to ["/node_modules/"] which means that by default nothing in node_modules gets transformed when Jest runs.

If you have a dependency in node_modules that needs to be transformed before running your unit tests then you will need to whitelist it with transformIgnorePatterns in your Jest config:

"transformIgnorePatterns": [
  "node_modules/(?!(module-that-needs-to-be-transformed)/)"
]