How To Use Esm Tests With Jest

Are you looking to level up your testing game and streamline your development process? Then, you're in the right place! Let's dive into how you can use ESM tests with Jest to ensure your code is top-notch and error-free.

ESM (ECMAScript Modules) is a modern standard for organizing and loading JavaScript code. Jest, on the other hand, is a popular testing framework that helps you automate your tests and catch bugs early on. By combining these two powerful tools, you can take your testing practices to new heights.

To get started with ESM tests in Jest, first, make sure you have Jest installed in your project. If you haven't already, you can do this using npm or yarn:

npm install --save-dev jest
# OR
yarn add --dev jest

Next, you'll want to set up Jest to support ESM tests. You can do this by adding the following configuration to your `package.json` file:

"jest": {
  "preset": "ts-jest/presets/default-esm"
}

This configuration tells Jest to use the `ts-jest` preset for ESM tests. Additionally, make sure to have the necessary dependencies installed by running:

npm install --save-dev ts-jest @types/jest
# OR
yarn add --dev ts-jest @types/jest

Once you've set up Jest for ESM tests, you can start writing your test files using the ESM syntax. For example, you can create a test file named `example.test.mjs` and write your test cases as follows:

// example.test.mjs
import { sum } from './math.js';

test('adds 1 + 2 to equal 3', () => {
  expect(sum(1, 2)).toBe(3);
});

In this example, we're importing a `sum` function from a `math.js` module and writing a test to ensure the function behaves as expected. Remember to use the `.mjs` extension for your test files to indicate that they are ESM modules.

To run your ESM tests with Jest, you can use the following command:

npx jest

Jest will automatically detect your test files and execute them, providing you with insightful feedback on the test results. You can also use Jest's CLI options to customize the test execution as needed.

By using ESM tests with Jest, you can take advantage of modern JavaScript features and streamline your testing process. Ensure your code is robust and reliable by writing comprehensive tests that cover all possible scenarios.

Now that you have the tools and knowledge to use ESM tests with Jest, go ahead and elevate your testing game. Happy testing!