Is it required for spring boot application to be connected to database when performing unit test

Question

I am writing unit test cases for service layer. This is my service class:

@Service
@RequiredArgsConstructor
public class EmpService {

    private final EmpRepository empRepository;

    public EmployeeDto findById(UUID id) {
        return empRepository.findById(id).map(this::mapToEmployeeDto);
    }
}

Test class:

@SpringBootTest
class EmpServiceTest {
    @Autowired
    EmpService empService;
    
    @MockBean
    EmpRepository empRepository;
    
    @Test
    void get_employee_by_id_success_case() throws IOException {

        UUID empId = UUID.fromString("2ec828f5-35d5-4984-b783-fe0b3bb8fbef"); 
        EmployeeDto expectedEmp = new EmployeeDto(empId, "James");
        EmployeeEntity stubbedEmployee = new EmployeeEntity(empId, "James");
        when(empRepository.findById(any(UUID.class)))
            .thenReturn(Optional.of(stubbedEmployee));
        EmployeeDto actualEmp = empService.findById(empId);
        assertEquals(expectedEmp, actualEmp);
    }
}

I am using docker images for my database (postgres). When the container is up for db, then the above test case runs successfully.

But when I stop the whole docker application, in that case it gives the following error:

java.lang.IllegalStateException: Failed to load ApplicationContext
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'empRepository' defined in repo.EmpRepository defined in @EnableJpaRepositories declared on JpaRepositoriesRegistrar.EnableJpaRepositoriesConfiguration: Cannot resolve reference to bean 'jpaMappingContext' while setting bean property 'mappingContext'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'jpaMappingContext': Invocation of init method failed; nested exception is javax.persistence.PersistenceException: [PersistenceUnit: default] Unable to build Hibernate SessionFactory; nested exception is org.hibernate.exception.JDBCConnectionException: Unable to open JDBC Connection for DDL execution

Shouldn't the unit test cases be independent from database, specially when we are mocking the repo bean?

Imagine a person takes fresh checkout of this code on their machine and builds the project first without setting up the db. In that case the unit tests should run and should not be dependent on database.

Please note I am using JUnit 5 (Jupiter), spring-boot-starter-test kit.

@Kayaman It is for code coverage. Right now application is in very infant stage. With time, more logic will be added to it. You can think that the test is to check if correct dto is returned in a happy scenario. — rsp
– rsp, Commented Sep 30, 2020 at 11:41
You have autowired EmpService which must be connecting to the repository. Try mocking EmpService. — Mudit Shukla
– Mudit Shukla, Commented Sep 30, 2020 at 12:50
@MS- If I do that then how will I call the method which I want to test — rsp
– rsp, Commented Sep 30, 2020 at 12:55
@SpringBootTest loads the application context that's why the bean creation fails. — Mudit Shukla
– Mudit Shukla, Commented Sep 30, 2020 at 13:44

Bartek Jablonski · Accepted Answer · 2020-09-30 12:46:02Z

1

In my opinion, what you write is more integration test, than unit one.

Apart for semantics, there is very nice framework named testcontainers, that will run database in docker container just for tests phase.

Here is article that shows how to set up such database tests: https://programmerfriend.com/spring-boot-integration-testing-done-right/

answered Sep 30, 2020 at 12:46

Bartek Jablonski

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