Configure Jest for a Node.js backend project

(P) Codever is an open source bookmarks and snippets manager for developers & co. See our How To guides to help you get started. Public bookmarks repos on Github ⭐🙏

The API supporting Codever is written in Node.js/ExpressJs, and I’ve decided to use Jest as the testing framework for unit testing. This blog post presents the steps required to install and run the first unit test in Jest for this backend.

Install Jest

Install npm dependency

Using npm run the following command

npm install --save-dev jest

This will install jest in the devDependencies in package.json of the backend project

Write a jest configuration file

In the root of the backend project create a jest.config.js configuration file with the following content:

module.exports = {
  testEnvironment: 'node',
  testMatch: ['**/*.spec.js'],
};

This tells the Jest runner to run all the files in the project ending in spec.js

Run first tests in Jest

In package.json under the scripts property define a test task for running jest tests - "test": "jest --config ./jest.config.js":

  "scripts": {
    "start": "node ./bin/www",
    "debug": "nodemon --inspect ./bin/www --watch src --watch docs/openapi/openapi.yaml",
    "test": "jest --config ./jest.config.js"
  },

With this configuration with npm run you can execute the script for running jest tests - npm run test

But for that we need to first write a Jest test. I will choose some utils methods used in searching bookmarks, snippets or notes to write first jest tests.

Let’s take the following method for example, from search.utils.js

let includeFulltextSearchTermsInFilter = function (fulltextSearchTerms, filter, searchInclude) {
  let newFilter = {...filter};
  if ( fulltextSearchTerms.length > 0 ) {
    let searchText = '';
    if ( searchInclude === 'any' ) {
      searchText = {$search: fulltextSearchTerms.join(' ')}
    } else {
      searchText = {$search: generateFullSearchText(fulltextSearchTerms)};
    }

    newFilter.$text = searchText;
  }
  return newFilter;
}

This method returns a new filter containing also the fulltext search depending on the OR or AND selection, but the best way to understand it, is looking at its corresponding test:

const searchUtils = require('./search.utils');

describe('includeFulltextSearchTermsInFilter', () => {
    test('returns filter with $text when fulltextSearchTerms is not empty', () => {
        const fulltextSearchTerms = ['testing jest'];
        const filter = {};
        const searchInclude = 'any';
        const expected = {
            ...filter,
            $text: {$search: fulltextSearchTerms.join(' ')}
        };
        expect(searchUtils.includeFulltextSearchTermsInFilter(fulltextSearchTerms, filter, searchInclude)).toEqual(expected);
    });

    test('returns filter without $text when fulltextSearchTerms is empty', () => {
        const fulltextSearchTerms = [];
        const filter = {};
        const searchInclude = 'any';
        expect(searchUtils.includeFulltextSearchTermsInFilter(fulltextSearchTerms, filter, searchInclude)).toBe(undefined);
    });
});

Now every time I run npm run test this test will also be executed. Easy peasy.

Source code for Codever.dev is available on Github - Star