Application style

In this application I demonstrate oppinionated style of writing backend application based on Java, Spring.

Integration Tests

Here I demonstrate how to use Testcontainers library to develop integration tests.

How to build the project

To build the project execute (including running integration tests and functional tests)

mvn clean install

How to run the application on localhost

java -jar target/application-style-exec.jar

Links

Zalando blog post

Personal blog post

Concept of integration tests with testcontainers.org library

testcontainers.org is a Java library that allows to run docker images and control them from Java code. (I will not cover topic what is Docker, if you need more information read more about it.)

The main concept of the proposal of the integration test is:

• Run your application
• Run external components as real docker containers. Here it is important to understand what I mean by external components. It can be:
  • database storage - for example run real PostgreSQL as docker image,
  • Redis - run real Redis as docker image,
  • RabbitMQ
  • AWS components like S3, Kinesis, DynamoDB and others you can emulate by localstack

Don't run another microservice as docker image. If you communicate with another microservice via HTTP, mock requests by mockserver run as docker images.

Your service comunicates with external components run as docker image.

Advantages

• You run tests against real components, for example H2 database doesn't support Postgres/MySQL specific functionality.
• You can run your tests offline - no Internet connection needed. It is an advantage for people who are traveling or if you have slow Internet connection.
• You can mock AWS services by localstack. It will simplify administrative actions, cut costs and make your build offline.
• You can test cornercases like:
  • simulate timeout from external service,
  • simulate wrong http codes,
• All tests are written by developers in the same commit.

Disadvantages

• Continuous integration (e.g. Jenkins) machine needs to be bigger (build uses more RAM and CPU).
• You need to run containers at least once - it consumes time and resources.

How to run Integration Tests

To run PostgreSQL you can add it to your test:

protected static PostgreSQLContainer postgreSQLContainer = new PostgreSQLContainer("postgres:11.2")
        .withUsername("userName")
        .withPassword("password")
        .withDatabaseName("experimentDB");

Then run database migration scripts (eg. Flyway). Even empty test will validate if your migrations are executed properly. As a good practice, you should remember about cleaning the state - delete inserted rows.

Example of DB IntegrationTest

    @BeforeEach
    void setUp() throws Exception {
        name = UUID.randomUUID().toString();
    }
    @AfterEach
    void tearDown() throws Exception {
        accountRepository.findByName(name)
            .ifPresent(account -> accountRepository.delete(account));
    }
    @Test
    void shouldFindByName() throws Exception {
        Account account = Account.builder()
            .name(name).additionalInfo("additionalInfo").build();
        accountRepository.save(account);
    }
    Optional<Account> actual = accountRepository.findByName(name);
        assertThat(actual.get()).isEqualTo(account);
    }

Disadvantages of testcontainer library

TestContainers support docker_compose file, but only version 2.0; while the docker_compose current version is 3.6.

Alternative solutions

I liked TestContainers library. Personally I find http://testcompose.com library more interesting. The main advantage is that it simply runs docker_compose file and reduces boilerplate code.

Note

In the example I used Java 17, whereas I always wait for a new release of Java