Boosting Test Performance With TestContainers

In my previous post on testing, I described how to use TestContainers to provide realistic test environments for database tests. This comment revealed the downside:

…as noted above, there always seems to be some drawback. In this case, the overhead of starting the Docker image and everything it contains will increase your overall build time.

As a reminder, here’s the TestContainer-specific code. Note the instance member postgres and the JUnit Rule that re-initializes it on a per-method basis:

package be.objectify.tcexample.db;

import be.objectify.tcexample.AbstractUserDaoTest;
import be.objectify.tcexample.UserDao;
import org.junit.After;
import org.junit.Before;
import org.junit.Rule;
import org.testcontainers.containers.PostgreSQLContainer;
import play.db.Database;

public class JooqUserDaoTest extends AbstractUserDaoTest implements DbTestSupport,
                                                                    TestData {

    @Rule
    public PostgreSQLContainer postgres = new PostgreSQLContainer();
    
    private Database database;
    
    @Before
    public void setup() throws Exception {
        // the database has all evolutions applied
        database = create(postgres); 
        // load some test data
        loadTestData(database); 
    }

    @After
    public void tearDown() {
        destroy(database);
    }

    @Override
    public UserDao dao() {
        return new JooqUserDao(database);
    }
}

Given that the huge increase in test duration results from Docker container start-up times, we can instead use a JUnit ClassRule to start up one container and re-use it for every test in the class. This means you should no longer run these tests in parallel, but the performance gains massively outweigh test parallelization.

package be.objectify.tcexample.db;

import be.objectify.tcexample.AbstractUserDaoTest;
import be.objectify.tcexample.UserDao;
import org.junit.After;
import org.junit.Before;
import org.junit.ClassRule;
import org.testcontainers.containers.PostgreSQLContainer;
import play.db.Database;

public class FasterJooqUserDaoTest extends AbstractUserDaoTest implements DbTestSupport,
                                                                          TestData {

    @ClassRule
    public static PostgreSQLContainer postgres = new PostgreSQLContainer();
    
    private Database database;
    
    @Before
    public void setup() throws Exception {
        database = create(postgres); 
        loadTestData(database); 
    }

    @After
    public void tearDown() {
        destroy(database);
    }

    @Override
    public UserDao dao() {
        return new JooqUserDao(database);
    }
}

The amount of time saved depends on the number of test methods in a class. I have some test classes that have upwards of 30 tests each, and in these cases, the execution time drops from minutes to seconds. Not bad for changing a couple of lines of code.