test process.env with Jest

Question

I have an app that depends on environmental variables like:

const APP_PORT = process.env.APP_PORT || 8080;

and I would like to test that fo

Answer 1

Jest's setupFiles is the proper way to handle this, and you need not install dotenv, nor use an .env file at all, to make it work.

jest.config.js:

module.exports = {
  setupFiles: ["<rootDir>/.jest/setEnvVars.js"]
};

.jest/setEnvVars.js:

process.env.MY_CUSTOM_TEST_ENV_VAR = 'foo'

That's it.

Answer 2

Expanding a bit on Serhan C.'s answer (https://stackoverflow.com/a/57944454/2708174)...

according to this blog https://tekloon.dev/using-dotenv-with-jest you can include "dotenv/config" directly in setupFiles, without having to create and reference an external script that calls require("dotenv").config().

i.e., simply do

module.exports = {
    setupFiles: ["dotenv/config"]
}

Answer 3

In ./package.json:

"jest": {
  "setupFiles": [
    "<rootDir>/jest/setEnvVars.js"
  ]
}

In ./jest/setEnvVars.js:

process.env.SOME_VAR = 'value';

Answer 4

In my opinion, it's much cleaner and easier to understand if you extract the retrieval of environment variables into a util (you probably want to include a check to fail fast if an environment variable is not set anyway), then you can just mock the util.

// util.js
exports.getEnv = (key) => {
    const value = process.env[key];
    if (value === undefined) {
      throw new Error(`Missing required environment variable ${key}`);
    }
    return value;
};

// app.test.js
const util = require('./util');
jest.mock('./util');

util.getEnv.mockImplementation(key => `fake-${key}`);

test('test', () => {...});

Answer 5

Another option is to add it to the jest.config.js file after the module.exports definition:

process.env = Object.assign(process.env, {
  VAR_NAME: 'varValue',
  VAR_NAME_2: 'varValue2'
});

This way it's not necessary to define the ENV variables in each .spec file and they can be adjusted globally.

Answer 6

I think you could try this too:

const currentEnv = process.env;
process.env = { ENV_NODE: 'whatever' };

// test code...

process.env = currentEnv;

This works for me and you don't need module things