I have found Embedded MongoDB library which looks quite promising and does what you have asked for.

Currently supports MongoDB versions: 1.6.5 to 3.1.6, provided the binaries are still available from the configured mirror.

Here is short example of use, which I have just tried and it works perfectly:

public class EmbeddedMongoTest { private static final String DATABASE_NAME = "embedded"; private MongodExecutable mongodExe; private MongodProcess mongod; private Mongo mongo; @Before public void beforeEach() throws Exception { MongoDBRuntime runtime = MongoDBRuntime.getDefaultInstance(); mongodExe = runtime.prepare(new MongodConfig(Version.V2_3_0, 12345, Network.localhostIsIPv6())); mongod = mongodExe.start(); mongo = new Mongo("localhost", 12345); } @After public void afterEach() throws Exception { if (this.mongod != null) { this.mongod.stop(); this.mongodExe.stop(); } } @Test public void shouldCreateNewObjectInEmbeddedMongoDb() { // given DB db = mongo.getDB(DATABASE_NAME); DBCollection col = db.createCollection("testCollection", new BasicDBObject()); // when col.save(new BasicDBObject("testDoc", new Date())); // then assertThat(col.getCount(), Matchers.is(1L)); } } 

There is Foursquare product Fongo. Fongo is an in-memory java implementation of mongo. It intercepts calls to the standard mongo-java-driver for finds, updates, inserts, removes and other methods. The primary use is for lightweight unit testing where you don't want to spin up a mongo process.

If you're using Maven you may be interested in a plugin I've created that wraps the flapdoodle.de 'embedded mongo' API:

embedmongo-maven-plugin

It provides a start goal that you can use to start any version of MongoDB you want (e.g. during pre-integration-test), and a stop goal that will stop MongoDB (e.g. during post-integration-test).

The real benefit of using this plugin over others is that there is no requirement for MongoDB to be installed beforehand. MongoDB binaries are downloaded and stored in ~/.embedmongo for future builds.

If you are using sbt and specs2, I wrote the same kind of wrapper for embedmongo

https://github.com/athieriot/specs2-embedmongo

with spring-boot 1.3 you can use EmbeddedMongoAutoConfiguration

pom.xml

<parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>1.3.2.RELEASE</version> </parent> ... <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-mongodb</artifactId> </dependency> <dependency> <groupId>de.flapdoodle.embed</groupId> <artifactId>de.flapdoodle.embed.mongo</artifactId> <version>${embedded-mongo.version}</version> </dependency> 

MongoConfig

@Configuration @EnableAutoConfiguration(exclude = { EmbeddedMongoAutoConfiguration.class }) public class MongoConfig{ } 

You can run MongoDB in memory as of version 3.2.6. From the site:

Starting in MongoDB Enterprise version 3.2.6, the in-memory storage engine is part of general availability (GA) in the 64-bit builds. Other than some metadata and diagnostic data, the in-memory storage engine does not maintain any on-disk data, including configuration data, indexes, user credentials, etc.

Not just for unit testing, but also explained how to use inmemory mongodb with rest api.

maven dependency:

 <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-mongodb</artifactId> </dependency> <dependency> <groupId>de.flapdoodle.embed</groupId> <artifactId>de.flapdoodle.embed.mongo</artifactId> </dependency> 

=============================================================================

application.properties

server.port = 8080 spring.data.mongodb.database=user_db spring.data.mongodb.port=27017 spring.data.mongodb.host=localhost 

=============================================================================

UserRepository.java

public interface UserRepository extends MongoRepository{

}

for reference and all java code use below link:(step by step explanation)

https://www.youtube.com/watch?v=2Tq2Q7EzhSA&t=7s

Performances are better when executing mongod with storageEngine='ephemeralForTest'

new MongodConfigBuilder() .version(Version.Main.PRODUCTION) .cmdOptions(new MongoCmdOptionsBuilder() .useStorageEngine("ephemeralForTest") .build()) .net(new Net("localhost", port, Network.localhostIsIPv6())) .build() 

To run Embedded mongodb for integration test following are the maven dependency needed:

 <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-mongodb</artifactId> <version>2.5.2</version> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-autoconfigure</artifactId> <version>2.5.2</version> </dependency> <dependency> <groupId>de.flapdoodle.embed</groupId> <artifactId>de.flapdoodle.embed.mongo</artifactId> <version>3.0.0</version> <scope>test</scope> </dependency> 

Try using below code snipped for EmbeddedMongoAutoConfiguration:

import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.boot.autoconfigure.mongo.MongoProperties; import org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration; import org.springframework.context.ApplicationContext; import org.springframework.context.annotation.Bean; @SpringBootApplication public class EmbeddedMongoApplication { public static void main(String[] args) { System.setProperty("os.arch", "x86_64"); SpringApplication.run(EmbeddedMongoApplication.class, args); } @Bean public EmbeddedMongoAutoConfiguration embeddedMongoAutoConfiguration(MongoProperties mongoProperties) { return new EmbeddedMongoAutoConfiguration(mongoProperties); } } 

Note:

Embedded mongodb will be downloaded to below Path. So take into consideration that path have proper permission.

Linux : $HOME/.embedmongo/linux/mongodb-linux-x86_64-3.2.2.tgz Windows : C:\Users\<username>\.embedmongo\win32\mongodb-win32-x86_64-3.x.x.zip 

In production, you will be using a real database.

If you want your tests to reflect how your product behaves in production, use a real instance of Mongo.

A fake implementation may not behave exactly the same as a real one. When testing, you should strive for correctness. Speed of execution comes second.