Spring Boot: example of base test class for testing Repositories

_SpringDataJpaIntegrationTest.java

package base;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.jdbc.AutoConfigureTestDatabase;
import org.springframework.boot.test.autoconfigure.orm.jpa.DataJpaTest;
import org.springframework.boot.test.autoconfigure.orm.jpa.TestEntityManager;
import org.springframework.test.context.ActiveProfiles;
import org.springframework.transaction.annotation.Transactional;
import org.springframework.transaction.support.TransactionTemplate;

import java.util.function.Consumer;
import java.util.function.Function;

import static org.springframework.boot.test.autoconfigure.jdbc.AutoConfigureTestDatabase.Replace;
import static org.springframework.transaction.annotation.Propagation.NOT_SUPPORTED;

/**
 * To be honest, I don't like to use the Spring Boot Test Slices (like {@code @DataJpaTest}, {@code @WebMvcTest} etc.).
 * I mean, I always try to favor using {@code @SpringBootTest} because it's closer to the real application, and
 * it's faster when running the whole test suite.
 */
@DataJpaTest // Starts persistence context only.
@Transactional(propagation = NOT_SUPPORTED) // Disables the default transactional context on each @Test method
@AutoConfigureTestDatabase(replace = Replace.NONE) // Uses the actual database instead of an in-memory database like H2
@ActiveProfiles("test") // Activates the testing profile (environment)
public abstract class SpringDataJpaIntegrationTest {

    /**
     * (!!!) It does NOT work properly when the transactional context is disabled. 
     *       You should use the repositories instead or combine it with TransactionTemplate for example.
     */
    @Autowired
    private TestEntityManager testEntityManager;

    @Autowired
    protected TransactionTemplate transactionTemplate;

    /**
     * Executes the function inside a transactional context and return its result
     */
    public <T> T doInTransaction(JpaTransactionFunction<T> function) {
        function.beforeTransactionCompletion();
        try {
            return transactionTemplate.execute(status -> {
                T result = function.apply(testEntityManager);
                return result;
            });
        } finally {
            function.afterTransactionCompletion();
        }
    }

    /**
     * Executes the function inside a transactional context but does not return anything
     */
    public void doInTransaction(JpaTransactionVoidFunction function) {
        function.beforeTransactionCompletion();
        try {
            transactionTemplate.executeWithoutResult(status -> {
                function.accept(testEntityManager);
            });
        } finally {
            function.afterTransactionCompletion();
        }
    }
    

    @FunctionalInterface
    protected interface JpaTransactionFunction<T> extends Function<TestEntityManager, T> {
        default void beforeTransactionCompletion() {}
        default void afterTransactionCompletion() {}
    }

    @FunctionalInterface
    protected interface JpaTransactionVoidFunction extends Consumer<TestEntityManager> {
        default void beforeTransactionCompletion() {}
        default void afterTransactionCompletion() {}
    }

}

BookRepositoryTest.java

package br.com.zup.edu.ifoodwebapp.samples.books;

import base.SpringDataJpaIntegrationTest;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.DisplayName;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.dao.DataIntegrityViolationException;
import org.springframework.transaction.TransactionSystemException;

import javax.validation.ConstraintViolation;
import javax.validation.ConstraintViolationException;
import java.util.Optional;

import static org.assertj.core.api.Assertions.*;
import static org.assertj.core.api.InstanceOfAssertFactories.iterable;
import static org.assertj.core.groups.Tuple.tuple;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertThrows;

class BookRepositoryTest extends SpringDataJpaIntegrationTest {
    
    @Autowired
    private BookRepository repository;

    @BeforeEach
    void setUp() {
        repository.deleteAll();
    }

    /**
     * (!!!) Example of how to use {@code TestEntityManager} with {@code doInTransaction()} methods
     */
    @Test
    @DisplayName("should find a book by ID")
    void t0() {
        // scenario
        Book book = new Book("9788550800653", "Domain-Driven Design", "DDD - The blue book");
        Long id = doInTransaction(em -> {
            return em.persistAndGetId(book, Long.class);
        });

        // action
        Optional<Book> found = repository.findById(id);

        // validation
        assertThat(found)
                .isPresent().get()
                .usingRecursiveComparison()
                .isEqualTo(book);
    }
    
    @Test
    @DisplayName("must save a book")
    void t1() {
        // scenario
        Book book = new Book("9788550800653", "Domain-Driven Design", "DDD - The blue book");

        // action
        repository.save(book);

        // validation
        assertThat(repository.findAll())
                .hasSize(1)
                .usingRecursiveFieldByFieldElementComparator()
                .containsExactly(book)
                ;
    }

    @Test
    @DisplayName("should not save a book with invalid parameters")
    void t2() {
        // scenario
        Book book = new Book("97885-invalid", "a".repeat(121), "");

        // action and validation
        assertThatThrownBy(() -> {
            repository.save(book);
        })
                .isInstanceOf(TransactionSystemException.class)
                .hasRootCauseInstanceOf(ConstraintViolationException.class)
                .getRootCause()
                .extracting("constraintViolations", as(iterable(ConstraintViolation.class)))
                .extracting(
                        t -> t.getPropertyPath().toString(),
                        ConstraintViolation::getMessage
                )
                .containsExactlyInAnyOrder(
                        tuple("isbn", "invalid ISBN"),
                        tuple("title", "size must be between 0 and 120"),
                        tuple("description", "must not be blank")
                )
        ;
        // Tip: Try always to verify the side effects
        assertEquals(0, repository.count());
    }

    @Test
    @DisplayName("should not save a book when a book with same isbn already exists")
    void t3() {
        // scenario
        String isbn = "9788550800653";
        Book ddd = new Book(isbn, "Domain-Driven Design", "DDD - The blue book");

        // action
        repository.save(ddd);

        // validation
        assertThrows(DataIntegrityViolationException.class, () -> {
            Book cleanCode = new Book(isbn, "Clean Code", "Learn how to write clean code with Uncle Bob");
            repository.save(cleanCode);
        });
        // Tip: Try always to verify the side effects
        assertEquals(1, repository.count());
    }

    @Test
    @DisplayName("should find a book by isbn")
    void t4() {
        // scenario
        String isbn = "9788550800653";
        Book book = new Book(isbn, "Domain-Driven Design", "DDD - The blue book");
        repository.save(book);

        // action
        Optional<Book> optionalBook = repository.findByIsbn(isbn);

        // validation
        assertThat(optionalBook)
                .isPresent().get()
                .usingRecursiveComparison()
                .isEqualTo(book)
                ;
    }

    @Test
    @DisplayName("should not find a book by isbn")
    void t5() {
        // scenario
        Book book = new Book("9788550800653", "Domain-Driven Design", "DDD - The blue book");
        repository.save(book);

        // action
        String notExistingIsbn = "1234567890123";
        Optional<Book> optionalBook = repository.findByIsbn(notExistingIsbn);

        // validation
        assertThat(optionalBook).isEmpty();
    }

}

• Spring Boot Test Slices: Overview and Usage
• Faster Spring Boot Testing with Test Slices
• Spring Docs: Auto-configured Data JPA Tests
• reflectoring.io: Testing JPA Queries with Spring Boot and @DataJpaTest
• reflectoring.io: Testing with Spring Boot and @SpringBootTest

That's how we can test our Service layer with @DatJpaTest:

@DataJpaTest(
    includeFilters = [
        ComponentScan.Filter(CreateBookService.class, type = ASSIGNABLE_TYPE)
    ]
)
class BookRepositoryTest {
    // ...
}

We can also use the @Import annotation instead:

@Import(CreateBookService.class)
class BookRepositoryTest extends SpringDataJpaIntegrationTest {
    // ...
}

Zalando Blog: Mastering Testing Efficiency in Spring Boot: Optimization Strategies and Best Practices