Embedded MongoDB provide a platform neutral way for running mongodb in Java unittests.

Thanks to this java library you can easily run integration test against a real mongo database. It is best to always mock your dependencies in true unit tests, but sometimes you need to test against the real thing.

• It will
  • download mongodb (and cache it)
  • extract it (and cache it)
  • java uses its process api to start and monitor the mongo process
  • you run your tests
  • java kills the mongo process

How to use it in your unit tests

Add the dependencies to your project

<dependency>
    <groupId>de.flapdoodle.embed</groupId>
    <artifactId>de.flapdoodle.embed.mongo</artifactId>
    <version>2.2.0</version>
    <scope>test</scope>
</dependency>

One way to ease the integration is to define your own annotation in MongoDbTest.java

import org.junit.jupiter.api.extension.ExtendWith;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@ExtendWith({
        MongoDbCallback.class
})
public @interface MongoDbTest {
}

And the following MongoDbCallback.java

public class MongoDbCallback implements BeforeAllCallback {
    private static MongodExecutable mongo;
    @Override public void beforeAll(ExtensionContext context) throws Exception {
        if (MONGO != null) {
            System.out.println("MongoDB already up and running");
        } else {
            var version = Version.Main.V4_0;
            var port = 27000;
            var config = new MongodConfigBuilder()
                    .version(version)
                    .net(new Net(port, Network.localhostIsIPv6()))
                    .build();
            mongo = MongodStarter.getDefaultInstance().prepare(config);
            mongo.start();
            System.out.println("Mongo started {} on port {}", version, port);
        }
    }
}

You can now annotate your integration test with @MongoDbTest and use the mongoClient connected to localhost:27000

Other ways to use Embedded MongoDB

• in a Maven build using maven-mongodb-plugin or embedmongo-maven-plugin
• in a Clojure/Leiningen project using lein-embongo
• in a Gradle build using gradle-mongo-plugin
• in a Scala/specs2 specification using specs2-embedmongo
• in Scala tests using scalatest-embedmongo