#gist-bookmark #jest #test #esm #alias #js

how-to-jest-esm.md

Jest added to project with aliasing and eslint rules. Jest is not supported esm & esm mocks yet, that's why we are forced to use jest-esm-transformer (Babel transform under the hood test modules & *.spec scripts to CommonJs). Without transform configuration we have error: SyntaxError: Cannot use import statement outside a module.

Nowadays (2022-01-12) we can esm without Babel only by ts-jest?

No! ts-jest uses Babel too and is only needed to catch additional type errors.

Read more:

• Pure ESM package gist
• Setting up Jest with ESM gist
• jest-clean-console-reporter
• awesome-jest#reporters
• ts-jest with old 2019 configuration for ts tested modules & ts tests
• another "boilerplate" ts-jest configuration
• StyleLint trying move to esm (jest too)
• Chromium headless & page model by Playwright ("Автотесты на базе playwright и jest")
• javascript-testing-best-practices
• nodejs-integration-tests-best-practices

All columns 100% except Func coverage, which is not 100%. Eslint no-empty-function should prevent this situation.
But how to code es5 static constructors?
Jest is not able to verify the empty function, because anonymous function is always created with new reference.

How to read Test Coverage report generated using Jest.

100% Func coverage is fixed by migrating from function to Object.

esm for Jest (also with Babel), classic way with @babel/preset-env solve import keyword errors:
package.json > scripts:
"test": "set NODE_ENV=envJest&&node -r esm ./node_modules/jest/bin/jest.js --runInBand --no-cache"

babel.config.json:

{
	"env": {
		"envJest": {
			"presets": ["@babel/preset-env"]
		}
	}
}

My solution with Babel.