Discover Hexagonal Architecture to create web applications with isolated, testable layers. Gain insights into designing clean, maintainable modules and advocating for suitable techniques for your application.

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This course will teach you all about creating a web application in the Hexagonal Architecture style. Hexagonal Architecture promotes the separation of concerns by encapsulating logic in different layers of the application. This enables a higher level of isolation, testability, and control over your business specific code. 

You will learn how to design software modules and complete applications in a clean and maintainable manner, while also learning how to advocate for a certain technique given your application and constraints.

By the end of this course, you will have a greater understanding of how to implement software architecture, a key skill for any senior developer.

Hexagonal Software Architecture for Web Applications

As we did for the web controller, it makes sense to cover persistence adapters with integration tests instead of unit tests since we not only want to verify the logic within the adapter, but also the mapping into the database.

# Account persistence adapter test

We want to test the persistence adapter we built in the chapter ["Implementing a Persistence Adapter"](https://www.educative.io/courses/hexagonal-architecture-web-apps/dependency-inversion-with-a-persistence-adapter).
The adapter has two methods, one for loading an `Account` entity from the database and another to save new account activities to the database:

@DataJpaTest
@Import({AccountPersistenceAdapter.class, AccountMapper.class})
class AccountPersistenceAdapterTest {

  @Autowired
  private AccountPersistenceAdapter adapter;
  
  @Autowired
  private ActivityRepository activityRepository;

  @Test
  @Sql("AccountPersistenceAdapterTest.sql")
  void loadsAccount() {
    Account account = adapter.loadAccount(
        new AccountId(1L), 
        LocalDateTime.of(2018, 8, 10, 0, 0));

    assertThat(account.getActivityWindow().getActivities()).hasSize(2);
    assertThat(account.calculateBalance()).isEqualTo(Money.of(500));
  }
  
  @Test
  void updatesActivities() {
    Account account = defaultAccount()
        .withBaselineBalance(Money.of(555L))
        .withActivityWindow(new ActivityWindow(
            defaultActivity()
                .withId(null)
                .withMoney(Money.of(1L)).build()))
        .build();
  
    adapter.updateActivities(account);
  
    assertThat(activityRepository.count()).isEqualTo(1);
  
    ActivityJpaEntity savedActivity = activityRepository.findAll().get(0);
    assertThat(savedActivity.getAmount()).isEqualTo(1L);
  }

}

# The `@DataJpaTest` annotation

With `@DataJpaTest`, we're telling Spring to instantiate the network of objects that are needed for
database access, including our Spring Data repositories that connect to the database. We add some additional 
`@Import`s to make sure that certain objects are added to that network. These objects are needed by
the adapter under test to map incoming domain objects into database objects, for instance.

In the test for the method `loadAccount()`, we put the database into a certain state using an #key# SQL: Structured Query Language #key# script. Then, we simply load the account through the adapter #key# API: Application Programming Interface #key# and verify that it has the state that we would expect it to have given the database state in the #key# SQL: Structured Query Language #key# script. 

The test for `updateActivities()` goes the other way around. We create an `Account` object with a new account activity and pass it to the adapter to persist. Then, we check if the activity has been saved to the database through the #key# API: Application Programming Interface #key# of `ActivityRepository`.



Learn how to test a persistence adapter with integration testing.

Before We Begin

What's Wrong with Layers?

Inverting Dependencies

Organizing Code

Implementing a Use Case

Implementing a Web Adapter

Implementing a Persistence Adapter

Testing Architecture Elements

Mapping Between Boundaries

Assembling the Application

Enforcing Architecture Boundaries

Taking Shortcuts Consciously

Assessment

Conclusion

Appendix

Testing a Persistence Adapter with Integration Tests

Account persistence adapter test