In this article, we will explore how to use Testcontainers
and Exposed, a lightweight ORM framework for Kotlin, to create a controlled environment for testing MySQL Database operations.
Setup a Kotlin project with gradle
First we install the latest gradle version using SDKMAN
sdk install gradle 8.1.1 Then create a new Gradle project using gradle init with Kotlin support
mkdir kotlin-project cd kotlin-project gradle init --type kotlin-application --dsl kotlin Add dependencies to gradle (build.gradle.kts)
// Exposed implementation("org.jetbrains.exposed", "exposed-core", "0.40.1") implementation("org.jetbrains.exposed", "exposed-dao", "0.40.1") implementation("org.jetbrains.exposed", "exposed-jdbc", "0.40.1") // MySQL JDBC Driver implementation("mysql:mysql-connector-java:8.0.19") // Connection pool implementation("com.zaxxer:HikariCP:5.0.1") // Test containers testImplementation("org.testcontainers:mysql:1.18.3") Define the entity using Exposed DAO flavor
Exposed supports DSL (Domain Specific Language) and DAO (Data Access Object).
The DAO flavor in Exposed is a lightweight ORM for performing CRUD operations on entities 1.
object Users: LongIdTable() { val name = varchar("name", 50) } class User(id: EntityID<Long>) : LongEntity(id) { companion object : LongEntityClass<User>(Users) var name by Users.name } LongIdTable uses an auto-incrementing Long primary key
Use Testcontainers to start MySQL container, and perform CRUD operations on User entity
We use a single test container to improve test speed by avoiding repetitive container startup and shutdown for every test or test-class
object TestDatabase { private val mySQLContainer: MySQLContainer<Nothing> = MySQLContainer<Nothing>("mysql:8.0.26").apply { withDatabaseName("test-db") withUsername("test-user") withPassword("test-password") start() // Start the container } init { val config = HikariConfig().apply { jdbcUrl = mySQLContainer.jdbcUrl username = mySQLContainer.username password = mySQLContainer.password driverClassName = "com.mysql.cj.jdbc.Driver" maximumPoolSize = 10 } val dataSource = HikariDataSource(config) // This doesn't connect to the database but provides a descriptor for future use // In the main app, we would do this on system start up // https://github.com/JetBrains/Exposed/wiki/Database-and-DataSource Database.connect(dataSource) // Create the schema transaction { SchemaUtils.create(Users) } } } We create a simple test to test the crud operations.
Note: To run the tests on your local machine, you must have Docker installed and running.
If you're using a Mac, you can use Docker Desktop for Mac.
@TestInstance(TestInstance.Lifecycle.PER_CLASS) class UserRepositoryTest { @BeforeAll fun setUp() { // Use the TestDatabase singleton to initialize the database TestDatabase } @Test fun crudUser() { transaction { // Create val newUser = User.new { name = "Alice" } // Read val retrievedUser = User.findById(newUser.id) assertEquals("Alice", retrievedUser?.name) // Update retrievedUser?.apply { name = "Bob" } val updatedUser = User.findById(newUser.id) assertEquals("Bob", updatedUser?.name) // Delete updatedUser?.delete() val deletedUser = User.findById(newUser.id) assertNull(deletedUser) } } } Summary
We've explored how to efficiently set up and automate Kotlin database testing using Testcontainers and the Exposed framework.
- Testcontainers allow us to run isolated database instance in Docker containers
- Exposed, with its lightweight DAO, make it easy to perform CRUD operations.
- Using a single test container throughout our test suit significantly improves performance.
You can find the complete source code for this tutorial on GitHub
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