Getting Started

For a working example of an application that uses mongoUnit for testing, see the following demo project: mongounit-demo2

Install with maven

To allow mongoUnit to do its magic, install it with maven by including it in your pom.xml dependencies.


NOTE: Currently, mongoUnit only supports Spring Boot projects, so your poml.xml has to be configured with Spring Boot.

Be sure to include <scope>test</scope> so mongoUnit only shows up in your test classpath.

See a complete example of pom.xml.

Older versions of Spring Boot

For Spring Boot version 3.x and above use mongoUnit 3.0.0, for Spring Boot version 2.3 and above, use mongoUnit version 2.0 and above. For earlier versions of Spring Boot, use mongoUnit version 1.1.0.

Annotate the test class with @MongoUnitTest

@DisplayName("MongoPersonDaoService with MongoUnit testing framework")
public class MongoPersonDaoServiceIT {

  private MongoPersonDaoService mongoPersonDaoService;

The @MongoUnitTest annotation causes a few things to happen automatically.

Be default, mongoUnit will create a database with URI of mongodb://localhost:27017/mongounit-testdb_yourUserName_yyyy_MM_dd_HH_mm_ss_randomHash. Also, now, before each test in this class, the database will be wiped by dropping all of its collections, ready to be seeded with the initial state data for the next test.

The database name is date/time stamped and randomized on purpose so multiple runs can happen in parallel without stepping on each other. For example, if the team has a single development server which is used by the Continous Integration server. In such a case, it’s common that several Pull Requests are getting verified and running at the same time.

Optinally annotate the test method with either @SeedWithDataset and/or @AssertMatchesDataset

While these annotations are optional, unless you are setting up initial database state manually with the methods from MongoUnit class, usually, these annotations are used.

Before any @SeedWithDataset annotations are placed, the database is 100% empty. While it’s possible that you’d want to start with an empty state, usually, you would want to populate the database with at least some initial data.

@DisplayName("Create person on a non-empty database")
void createPersonWithExistingData() {

  CreatePersonRequest request = CreatePersonRequest.builder()
      .address(Address.builder().street("13 Builder St.").zipcode(12345).build())
      .favColors(Arrays.asList("blue", "white"))


Both annotations (@SeedWithDataset and @AssertMatchesDataset) rely on some JSON file(s) which contain the actual data.

By default, mongoUnit will look for the JSON file based on the path mirroring the fully qualified test class path (including the class name itself as the deepest directory name) together with the method name.

By default, @SeedWithDataset will look for a file named in the format of methodName-seed.json and @AssertMatchesDataset will look for a file named in the format of methodName-expected.json.

For example, if the test class annotated with @MongoUnitTest is org.mongounit.demo.dao.mongo.MongoPersonDaoServiceIT, the @SeedWithDataset annotation on the createPersonWithExistingData will look for a file located at /org/mongounit/demo/dao/mongo/MongoPersonDaoServiceIT/createPersonWithExistingData-seed.json and the @AssertMatchesDataset annotation on the same method will look for a file located at /org/mongounit/demo/dao/mongo/MongoPersonDaoServiceIT/createPersonWithExistingData-expected.json.

Note that both paths start with a /, which signifies the classpath root.

Generate JSON snapshot of the database

mongoUnit comes with a utility that allows you to create the seed.json file from an existing database.

The usual process is for you to populate the database (either with some tool or by running a single test), inspect the database to verify it’s close to the state you want and then run the mongoUnit provided utility to generate the JSON file representing the entire database.

You can download the dataset generator utility from maven central.

For all of its available options see Dataset Generator section.

To use it with its minimal customizations:

$ java -jar mongounit-3.0.0-jar-with-dependencies.jar -dbUri=mongodb://localhost:27017/yourDbName

**** JSON was written to /.../output.json

This utility only reads from the database. It does not write anything to the database.

Once the output.json is generated, you can place it into the proper directory (e.g., src/test/resources/org/mongounit/demo/dao/mongo/MongoPersonDaoServiceIT/ and name it appropriately.

The same process can be followed to generate the JSON file that would represent the “post” test execution database state. Alternatively, you can take the previously generated seed file, copy it, rename it, and modify it to the state you expect the database to be after the test execution.

Please see Seed & Assertion JSON Formats for more details.

Pay particular attention to the Special Rule for Assertions