Java repositories testing


A few days ago I’ve stumbled upon SQL query performance issue. Git claims that I was the author so maybe that’s the reason I remember this feature. There was like 3 classes, everything was super easy and super fast all I needed to do was to let Hibernate do its thing. Then time passed, new features were requested, the model becomes more complex, the number of rows increased to ~4 million and original query became too slow.

When working on query optimization I was really happy to find that detailed tests are in place. With proper test setup I was able to test my new query to make sure all requirements are met and then quickly copy paste query to sqldeveloper run it on a test environment and verify if performance is acceptable. It wasn’t simple query and it took me some time to figure out how to make it quick and work exactly as old one. That was the time I was really glad that we invested in detailed unit tests in the beginning.


It’s possible to tests java repositories easily and you should do it.


Great presentation (polish) about database testing:

Few key points from Piotr’s presentation:

  • Do not touch production database (no inserts, updates etc).
  • It’s ok to use h2 on developer machine (you can create workarounds for unsupported features)
  • Your test database should be setup using production migration script (not Hibernate’s create-drop)
  • Automate as much as possible (from CI env to production like database setup)
  • Keep you migrations history straight (no out of order migrations)

I’d add few more points:

  • Test your application against production database (it’s ok to use h2 on localhost, but CI must execute tests on production database)
  • On test/integration env run your application with production like database state (everything will work fast with 10 records)
  • Treat your repository layer like everything else. You are testing your business logic in domain or services for sure. Is there any reason why you should skip repositories layer?
  • Make sure it’s easy to setup production like environment on localhost (docker, vagrant whatever the point is it should be possible, easy and fast)


Piotr in his presentation does not show a lot of code samples. In order to verify how this approach works with spring-boot (which I avoid in complex applications) I decided to create very simple project which will demonstrate how to write tests for repository layer.

We are talking about the spring-boot application with hibernate and flyway. The assumption is that flyway is responsible for database setup on production, and since it’s configuring DB on production it will setup database for tests. I’m going to use two databases. PostgreSQL for production like environment and H2 for local development. Tests and application will work on both databases.

The model will be very simple. Two classes:

@Table(name = "user_")
@ToString(exclude = {"password", "roles"})
public class User {
  @GeneratedValue(strategy = GenerationType.SEQUENCE)
  private Long id;

  private String login;

  private String password;

  private Set<Role> roles = new HashSet<>();

public class Role {
  @GeneratedValue(strategy = GenerationType.SEQUENCE)
  private Long id;

  private String name;

Two simple repositories:

public interface RoleRepository extends JpaRepository<Role, Long> { }

public interface UserRepository extends JpaRepository<User, Long> {

  @Query("from #{#entityName} where lower(login) = lower(:login) and password = :password")
  User login(
    @Param("login") String login,
    @Param("password") String password);

  @Query("select case " +
         "  when count(u) > 0 then true " +
         "  else false " +
         "end " +
         "from #{#entityName} u " +
         "join u.roles roles " +
         "where " +
         "  u.login = :login " +
         "  and :role in(roles)")
  boolean userHasRole(
    @Param("login") String login,
    @Param("role") Role role);

Nothing interesting in RoleRepository and not much in UserRepository but complexity is not the point here.

class UserRepositoryTest extends RepositorySpecification {
  UserRepository userRepository

  RoleRepository roleRepository

  def "should login user by exact password match"() {
    final password = "pass"
    final user = userRepository.saveAndFlush(new User(login: "login", password: password))

    userRepository.login(user.login, password).id ==

    userRepository.login(user.login, password.toUpperCase()) == null

  def "login should be case insensitive"() {
    final user = new User(login: "newuser", password: "newuser")

    final loggedUser = userRepository.login("NEWUser", "newuser")

    loggedUser.login == user.login

  def "should detect if user has role"() {
    final role = new Role(name: "role 1")
    final otherRole = new Role(name: "otherRole")
    final user = new User(
      login: "login",
      password: "password",
      roles: [role] as Set)

    and:[role, otherRole])

    userRepository.userHasRole(user.login, role) == true
    userRepository.userHasRole(user.login, otherRole) == false

Now we have tests which will fail in case of query change. It is safe to refactor and optimize. We are also future proof in case of any DB or model change we will know from CI tool when something is wrong. What’s more, with few additional steps we will be able to make sure everything will work on the production like DB.

To make it (almost) work all we need to do is to introduce RepositorySpecification:

@TestPropertySource(properties = [",test"])
abstract class RepositorySpecification extends Specification {
  static class TestConfiguration {
    public FlywayMigrationStrategy migrationStrategy() {
      return { flyway ->

That’s all repository specification is ready. Not much here either. We create test spring context and we use custom FlywayMigrationStrategy to make sure that Postgres is cleared before migrations.

Now we are almost ready to go there is only one additional step. We need configuration:

# = dev

spring.jpa.hibernate.ddl-auto = validate = true

flyway.locations = ${db.migrations}

Note that by default we are running with dev profile and we load flyway migrations from the property named db.migrations.

spring.jpa.hibernate.ddl-auto = none

spring.datasource.url = jdbc:h2:mem:tmp
spring.datasource.username = sa
spring.datasource.password =

db.type = h2
db.migrations = db/migrations/core

dev profile means that we run on in memory h2 database and we skip schema validation.

spring.datasource.url = jdbc:postgresql://localhost:5432/postgres
spring.datasource.username = postgres
spring.datasource.password = secretpassword

db.type = postgres
db.migrations = db/migrations/core

Postgres profile differs only in DB connection details. But you can load custom migrations scripts on h2 and completely different on Postgres. You can easily implement custom scripts which will work with both databases. There is more. On dev environment you can load sample data to fill up the database with something which will make the application look like alive system.

The last step is database truncate before tests. If you load data as migrations step we should get rid of it to make sure that your tests are not coupled with test data which might be modified in the future.

flyway.locations = ${db.migrations},db/migrations/truncate/${db.type}

When running test profile all we need is default DB setup for “parent” profile with one additional step - truncate database. With db.type property it’s possible to load dedicated scripts responsible for DB truncating. DB (truncate scripts are in git).

in order to run tests against h2 db all you need to do is: ./gralew test which is the same to running: ./gradlew test,test It’s easy to start tests on Postgres: ./gradlew test,test On localhost you will be able to work fast (applying 100+ migrations to in memory H2 is faster than working with traditional DB) and your CI environment will handle testing application on the production like DB.


With this pretty simple setup you can test your application against h2 and Postgres database. In case of local environment and simple changes you will not need to bother yourself with Postgres. It might be easy for you to run your application on Postgres in docker on Linux, but using docker on windows is not as continent (try to explain to CSS magician that he needs to install virtual box, than docker, then run Postgres in docker in order to fix up text alignment).

See Also

If you've enjoyed or found this post useful you might also like:

6 Nov 2016 #tdd #spring #hibernate #flyway