jest-environment-mongodb

Easily run Jest integration tests that require a running MongoDB server

Features

• Superfast in watch mode (use --runInBand to prevent MongoDB from rebooting between test-runs)
• Easy to set the storage engine per test file (use docblocks to override the default storage engine on a per file basis)
• Includes TypeScript type annotations

Types

This package is written in TypeScript, type declarations (and source maps) are included with the package so no need to install types separately. It also works great with regular JavaScript.

Installation

NPM

npm install --save-dev mongodb-memory-server jest-environment-mongodb

Yarn

yarn add --dev mongodb-memory-server jest-environment-mongodb

Configuration - configuration file

To use jest-environment-mongodb as the default test environment, update your Jest configuration as follows:

{
  "testEnvironment": "mongodb"
}

To set the test environment on a per file or file pattern basis, consider using a docblock (see the next section) or configure Jest projects.

Configuration - docblock

By adding a @jest-environment docblock at the top of a test file, you can specify mongodb to be used for all tests in that file:

/**
 * @jest-environment mongodb
 */

This overrides any environment set by testEnvironment in the Jest configuration file.

For docblock usage, jest-environment-mongodb-wiredtiger and jest-environment-mongodb-ephemeral may come in handy.

Default mode

The default behavior of jest-environment-mongodb is to run one MongoDB server per Jest worker and to set up a new database for each test suite. This means you have complete isolation between test suites and parallel test runs (workers). While great for running many tests (in for example CI), it is also slow, especially if you need to apply indexes to your collections. This becomes particularly painful if you use watch mode when developing. However, you can change this behavior with --runInBand, which will keep a single server running between test runs, see the next section.

TDD mode - keeping the MongoDB server alive between test suites

When starting Jest with the --runInBand (or the alias -i) CLI flag, a single MongoDB server will be started and kept alive between test runs. This is useful when running Jest in watch mode, as it prevents MongoDB from restarting between every code change.

If you need to apply indexes to your DB before running tests, --runInBand will give you an extra performance boost since you don't need to recreate the indexes for every code-change/test-run.

The MongoDB server is also kept alive and shared between test suites.

Just remember to clean up your database between each test and this should give a nice performance boost when developing.

Example:

jest --watch --runInBand mytests.test.js

MongoDB server options

Configure the MongoDB server by passing options to testEnvironmentOptions of your Jest configuration file.

The available testEnvironmentOptions are the same as the mongodb-memory-server options.

Example:

{
  "testEnvironment": "mongodb",
  "testEnvironmentOptions": {
    "binary": {
      "version": "3.6.5"
    },
    "instance": {
      "storageEngine": "wiredTiger"
    }
  }
}

MongoDB options provided via testEnvironmentOptions also applies to docblock environments.

Globals

The jest-environment-mongodb environment exposes three global variables:

global.MONGO_URI      // The server connection URI
global.MONGO_DB_NAME  // The database name
global.MONGOD         // The mongod instance from `mongodb-memory-server`

Usage

/**
 * @jest-environment mongodb
 */

import { MongoClient } from "mongodb";

let client;
let db;

beforeAll(async () => {
  client = await MongoClient.connect(global.MONGO_URI);
  db = await client.db(global.MONGO_DB_NAME);
});

afterAll(async () => {
  await client.close();
});

beforeEach(async () => {
  // Reset the database before each test
  await db.dropDatabase();
});

it("should aggregate docs from collection", async () => {
  const files = db.collection("files");

  await files.insertMany([
    { type: "Document" },
    { type: "Video" },
    { type: "Image" },
    { type: "Document" },
    { type: "Image" },
    { type: "Document" },
  ]);

  const topFiles = await files
    .aggregate([
      { $group: { _id: "$type", count: { $sum: 1 } } },
      { $sort: { count: -1 } },
    ])
    .toArray();

  expect(topFiles).toEqual([
    { _id: "Document", count: 3 },
    { _id: "Image", count: 2 },
    { _id: "Video", count: 1 },
  ]);
});

See also

• jest-environment-mongodb-wiredtiger
• jest-environment-mongodb-ephemeral