H fun tests in Spring

Hello, dear Java warrior! ? If you are here, then it’s time to get on the testing path and prove that your code works better than what marketers promise. Today we will talk about testing logic in Spring using an H2 database. Let's go! ?

Why do we need H2?

Imagine: you are writing the coolest service, but you are afraid that your business logic lives in a world of illusions. You don't want tests to drive the real database because:

1. It's slow.
2. It's risky (deleting something by accident? We're not like that!).
3. This is too realistic, and H2 is our matrix, where everything is under control. H2 is your friend code:

• Lightweight.
• Built-in.
• Ideal for tests.

Setting up application.properties: let H2 do the work for you

Before we start, let's prepare our cozy test little world. To do this, we will write the necessary settings in src/test/resources/application.properties. Voila:

# Подключаем H2
spring.datasource.url=jdbc:h2:mem:testdb;DB_CLOSE_DELAY=-1;DB_CLOSE_ON_EXIT=FALSE
spring.datasource.driver-class-name=org.h2.Driver
spring.datasource.username=sa
spring.datasource.password=password

# Убедимся, что Hibernate всё за нас делает
spring.jpa.hibernate.ddl-auto=create-drop
spring.jpa.database-platform=org.hibernate.dialect.H2Dialect

What does this all mean?

spring.datasource.url: indicates that we want to use an "in-memory" database (mem:testdb), which will disappear as soon as we turn off the tests.
DB_CLOSE_DELAY=-1: the database will live until the end of the JVM (long live stability!).
spring.jpa.hibernate.ddl-auto=create-drop: we create a database when running tests, delete it after. Cleanliness is the key to success.

Adding dependencies

For Maven

<dependency>
    <groupId>com.h2database</groupId>
    <artifactId>h2</artifactId>
</dependency>

For Gradle

implementation 'com.h2database:h2'

Setting up tests

Now let's write our tests. We turn on Spring, the magic of annotations and a little love for code.

Example: Adding a user

Let's say we have a User entity:

# Подключаем H2
spring.datasource.url=jdbc:h2:mem:testdb;DB_CLOSE_DELAY=-1;DB_CLOSE_ON_EXIT=FALSE
spring.datasource.driver-class-name=org.h2.Driver
spring.datasource.username=sa
spring.datasource.password=password

# Убедимся, что Hibernate всё за нас делает
spring.jpa.hibernate.ddl-auto=create-drop
spring.jpa.database-platform=org.hibernate.dialect.H2Dialect

Testing adding a user

<dependency>
    <groupId>com.h2database</groupId>
    <artifactId>h2</artifactId>
</dependency>

What's going on here?

@SpringBootTest: Raising the Spring context (everything is like in production, but safe).
@Autowired: Dependency injection because we deserve it.
UserRepository: your repository works like in battle.

Results

Now you know how to create friendship between Spring, H2 and tests. These examples are your key to a world where there are no bugs and tests work the first time. Don't forget: tests don't make your code better, but they do help you sleep soundly. Good luck! ?

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