Key points

Babel

• Add babel.config.js
• Create a custom Babel environment for tests called test.
• Use the transform-es2015-modules-commonjs plugin for your test Babel environment.

Jest

• Create a jest.config.js file.
• Add a transform property to your jest.config.js file. This way all files matching the pattern will be transformed using the module you provide (with Babel in our case: babel-jest).
• Run your tests with NODE_ENV=test, so your Jest run is associated with the test Babel environment.
• Run yarn test to run tests.