Configure Jest and usage in UmiJS 🥳
Tags: webdev, javascript, testing, umijs
Published: 2023-01-12 12:54:37

Before setting up Jest and using it in your application,
you can initiate a umijs project using the following
```
yarn create @umijs/umi-app
```

## To configure Jest in umi.js, you will need to install the following dependencies:

- [jest](https://jestjs.io/) and [@testing-library/react](https://testing-library.com/docs/react-testing-library/intro/): These are the core libraries needed for running tests and testing React components.

- [babel-jest](https://www.npmjs.com/package/babel-jest): This library is needed to enable Jest to understand modern JavaScript syntax.

- @umijs/preset-jest: This is a preset that provides a set of Jest configurations that are optimized for umi.js.


![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/b30nnei7fgigjtjijg64.png)

Once you have installed these dependencies, you can add a jest field to the package.json file in your project's root directory. This field should contain the following configurations:

```
{
  "jest": {
    "preset": "@umijs/preset-jest"
  }
}
```

You also need to add jest script in package.json

```
"scripts": {
    "test": "jest"
  }
```

And then you can run the test cases via npm run test

You can also configure Jest with a configuration file, `jest.config.js`, in the project's root directory. This file should export an object that contains the Jest configurations.

Make sure you have the correct imports and presets in your `jest.config.js` file.

```
const { presets } = require('@umijs/preset-jest');
module.exports = {
  ...presets,
  testMatch: ['<rootDir>/tests/**/*.test.js'],
};
```

This should get you started with Jest in umi.js.

## To write unit tests in umi.js, you can use Jest as the test runner and React testing library as the testing library.

- Create a __tests__ folder in your project, and create a test file for the component you want to test (e.g. MyComponent.test.js).

- Import the component you want to test and the Enzyme library at the top of the test file:
```
import React from 'react';
import { render } from '@testing-library/react';
import MyComponent from './MyComponent';
```
- Write your test cases using Jest and Enzyme. For example, you can test if the component renders correctly by doing the following:
```
describe('MyComponent', () => {
  it('should render the component', () => {
    const { getByText } = render(<MyComponent />);
    const text = getByText(/Hello, World!/i);
    expect(text).toBeInTheDocument();
  });
});

```
- Finally, you can run the tests by running the following command:

```
npx jest
```

Make sure you have the jest configuration file in your project root directory. If not, you can create one with the command `jest --init` or creating a file called jest.config.js in the root of your project with the following content:
```
module.exports = {
  "setupFilesAfterEnv": ["<rootDir>/setupTests.js"]
}
```

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