memongo is a Go package that spins up a real MongoDB server, backed by in-memory storage, for use in testing and mocking during development. It's based on mongodb-memory-server for NodeJS and memongo for Go.

In general, it's better to mock out interaction with the database, so you don't need to run a Mongo server during testing. But because most Mongo clients use a fluent interface that's tough to mock, and sometimes you need to test the queries themselves, it's often helpful to be able to spin up a Mongo server quickly and easily. That's where memongo comes in!

Project Status

Beta. Tests and CI are set up and working, but more esoteric configurations may not work. If memongo isn't working on your platform, you might want to use memongo.StartWithOptions() and pass the correct download URL for your platform manually.

Caveats and Notes

Currently, memongo only supports UNIX systems. CI will run on MacOS, Ubuntu Xenial, Ubuntu Trusty, and Ubuntu Precise. Other flavors of Linux may or may not work.

Basic Usage

Spin up a server for a single test:

func TestSomething(t *testing.T) {
  mongoServer, err := memongo.Start("4.0.5")
  if (err != nil) {
    t.Fatal(err)
  }
  defer mongoServer.Stop()

  connectAndDoStuff(mongoServer.URI(), memongo.RandomDatabase())
}

Spin up a server, shared between tests:

var mongoServer memongo.Server;

func TestMain(m *testing.M) {
  mongoServer, err = memongo.Start("4.0.5")
  if (err != nil) {
    log.Fatal(err)
  }
  defer mongoServer.Stop()

  os.Exit(m.Run())
}

func TestSomething(t *testing.T) {
  connectAndDoStuff(mongoServer.URI(), memongo.RandomDatabase())
}

Spin up a replica set server:

var mongoServer memongo.Server;

func TestMain(m *testing.M) {
  mongoServer, err = memongo.StartWitOptions(&memongo.Options{MongoVersion: "4.2.1", ShouldUseReplica: true})
  if (err != nil) {
    log.Fatal(err)
  }
  defer mongoServer.Stop()

  os.Exit(m.Run())
}

func TestSomething(t *testing.T) {
  connectAndDoStuff(mongoServer.URI(), memongo.RandomDatabase())
}

How it works

Behind the scenes, when you run Start(), a few things are happening:

1. If you specified a MongoDB version number (rather than a URL or binary path), memongo detects your operating system and platform to determine the download URL for the right MongoDB binary.

2. If you specified a MongoDB version number or download URL, memongo downloads MongoDB to a cache location. For future runs, memongo will just use the copy from the cache. You only need to be connected to the internet the first time you run Start() for a particular MongoDB version.

3. memongo starts a process running the downloaded mongod binary. It uses the ephemeralForTest storage engine, a temporary directory for a dbpath, and a random free port number.

4. memongo also starts up a "watcher" process. This process is a simple portable shell script that kills the mongod process when the current process exits. This ensures that we don't leave behind mongod processes, even if your tests exit uncleanly or you don't call Stop().

Configuration

The behavior of memongo can be controlled by using memongo.StartWithOptions instead of memongo.Start. See the godoc for all the options. Many options can also be set via environment variable.

A few common use-cases are covered here:

Note that you must use MongoDB version 3.2 or greater, because the ephemeralForTest storage engine was not present before 3.2.

Set the cache path

memongo downloads a pre-compiled binary of MongoDB from https://www.mongodb.org and caches it on your local system. This path is set by (in order of preference):

• The CachePath passed to memongo.StartWithOptions
• The environment variable MEMONGO_CACHE_PATH
• If XDG_CACHE_HOME is set, $XDG_CACHE_HOME/memongo
• ~/.cache/memongo on Linux, or ~/Library/Caches/memongo on MacOS

Override download URL

By default, memongo tries to detect the platform you're running on and download an official MongoDB release for it. If memongo doesn't yet support your platform, of you'd like to use a custom version of MongoDB, you can pass DownloadURL to memongo.StartWithOptions or set the environment variable MEMONGO_DOWNLOAD_URL.

memongo's caching will still work with custom download URLs.

Use a custom MongoDB binary

If you'd like to bypass memongo's download beahvior entirely, you can pass MongodBin to memongo.StartWithOptions, or set the environment variable MEMONGO_MONGOD_BIN to the path to a mongod binary. memongo will use this binary instead of downloading one.

If you're running on a platform that doesn't have an official MongoDB release (such as Alpine), you'll need to use this option.

Reduce or increase logging

By default, memongo logs at an "info" level. You may call StartWithOptions with LogLevel: memongolog.LogLevelWarn for fewer logs, LogLevel: memongolog.LogLevelSilent for no logs, or LogLevel: memongolog.LogLevelDebug for verbose logs (including full logs from MongoDB).

By default, memongo logs to stdout. To log somewhere else, specify a Logger in StartWithOptions.