Testcontainers with Spring Boot and Java 11/17

What are Testcontainers?

Testcontainers is a JVM library that allows users to run and manage Docker images and control them from Java code. The integration test additionally runs external components as real Docker containers.

Databases - Run PostgreSQL as a Docker image
Mocked HTTP server - HTTP services by using MockServer or WireMock Docker images
Redis - run real Redis as a Docker image,
Message Brokers - RabbitMQ
AWS - S3, DynamoDB etc
Any other application that can be run as a Docker image

How to use?

Setup : Spring Boot and Junit 5
Dependency to testImplementation "org.testcontainers:postgresql:1.16.2” and testImplementation "org.testcontainers:junit-jupiter:1.16.2”
And then some wireing to start testcontainers and link them to the test context so that integration tests knows where to look for the containers.

Example Abstract Class for setup

package com.test;

import org.springframework.boot.test.autoconfigure.jdbc.AutoConfigureTestDatabase;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.context.ApplicationContextInitializer;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.PropertySource;
import org.springframework.test.context.ActiveProfiles;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.support.TestPropertySourceUtils;
import org.springframework.test.web.servlet.request.MockHttpServletRequestBuilder;
import org.testcontainers.containers.PostgreSQLContainer;
import org.testcontainers.ext.ScriptUtils;
import org.testcontainers.jdbc.JdbcDatabaseDelegate;
import org.testcontainers.junit.jupiter.Testcontainers;
import org.testcontainers.shaded.com.fasterxml.jackson.databind.ObjectMapper;
import org.testcontainers.shaded.com.fasterxml.jackson.databind.SerializationFeature;

import java.util.Optional;

import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.post;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.put;


@Testcontainers
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT, classes = {com.test.Application.class})
@ActiveProfiles(AbstractBaseIntergrationTestConfiguration.ACTIVE_PROFILE_NAME_TEST)
@AutoConfigureTestDatabase(replace = AutoConfigureTestDatabase.Replace.NONE)
@ContextConfiguration(initializers = AbstractBaseIntergrationTestConfiguration.DockerPostgreDataSourceInitializer.class)
public abstract class AbstractBaseIntergrationTestConfiguration {

    protected static final String JDBC_URL = "jdbc.url=";
    protected static final String JDBC_USERNAME = "jdbc.username=";
    protected static final String JDBC_PASSWORD = "jdbc.password=";
    protected static final String JDBC_DRIVER_CLASS_NAME_ORG_POSTGRESQL_DRIVER = "jdbc.driverClassName=org.postgresql.Driver";
    protected static final String ACTIVE_PROFILE_NAME_TEST = "TestContainerTests";

    //--
    public static PostgreSQLContainer<?> postgreDBContainer;
    protected ObjectMapper objectMapper = new ObjectMapper().disable(SerializationFeature.FAIL_ON_EMPTY_BEANS);

    static {
        // Init DB Script here
        postgreDBContainer = new PostgreSQLContainer<>(IntegrationTestConstants.POSTGRESQL_IMAGE);
        postgreDBContainer
                .withInitScript(IntegrationTestConstants.INIT_DB_SCRIPT)
                .withDatabaseName(IntegrationTestConstants.DB_NAME)
                .withUsername(IntegrationTestConstants.DB_USERNAME)
                .withPassword(IntegrationTestConstants.DB_PASSWORD);

        postgreDBContainer.start();
        var containerDelegate = new JdbcDatabaseDelegate(postgreDBContainer, "");

        // Adding Database scripts here
        ScriptUtils.runInitScript(containerDelegate, IntegrationTestConstants.MISSING_TABLES_SQL);
        ScriptUtils.runInitScript(containerDelegate, IntegrationTestConstants.SAMPLE_DATA_SQL);
    }

    // This class adds the DB properties to Testcontainers.
    public static class DockerPostgreDataSourceInitializer implements ApplicationContextInitializer<ConfigurableApplicationContext> {

        @Override
        public void initialize(ConfigurableApplicationContext applicationContext) {

            TestPropertySourceUtils.addInlinedPropertiesToEnvironment(
                    applicationContext,
                    JDBC_DRIVER_CLASS_NAME_ORG_POSTGRESQL_DRIVER,
                    JDBC_URL + postgreDBContainer.getJdbcUrl(),
                    JDBC_USERNAME + postgreDBContainer.getUsername(),
                    JDBC_PASSWORD + postgreDBContainer.getPassword()
            );
        }
    }
}

How to write a test?

@Test
void checkIfUserExistInIdealCase() throws Exception {
  final JSONObject request = new JSONObject();
  
  request.put("email", "abc@test.com");
  
  final MockHttpServletRequestBuilder postObject = getPostRequestExecutorBuilder("http://localhost:8080/v1/checkemail/", Optional.empty());
  final MvcResult result = mockMvc.perform(postObject.content(request.toString())).andExpect(status().isOk()).andReturn();
  final String content = result.getResponse().getContentAsString();
  
  final SyncResponseDto responseDto = objectMapper.readValue(content, SyncResponseDto.class);
  
  assertThat(responseDto.getResponseReturnCode()).isEqualTo(ResponseReturnCode.USER\_EXIST);
}

Advantages

Run Integration Tests offline.
You run tests against real components, PostgreSQL database instead of the H2 database.
You can mock AWS services.
Implementation and tests can be written by developers same time when raising a PR.
Multiple containers can be added and it’s consistent across all developer machines. Same versions etc and runs without any efforts with GitHub actions.

Disadvantages
The main limitation is, that containers cannot be reused between test classes.
Adding “one more” external dependency.
Takes a bit more time than usual to start a container, 4 - 5 seconds for Postgres VS 0.5 seconds for H2.
When running locally, local machine should be powerful enough too ;)
More RAM, More Power as multiple containers can be run.