AssertJ: Example of a jUnit5 test for asserting Bean Validation errors thrown by Spring Boot Repository

_BookRepositoryTest.java

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.boot.test.context.SpringBootTest;
import org.springframework.dao.DataIntegrityViolationException;
import org.springframework.test.context.ActiveProfiles;
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.*;

@SpringBootTest
@ActiveProfiles("test")
class BookRepositoryTest {

    @Autowired
    private BookRepository repository;

    @BeforeEach
    void setUp() {
        repository.deleteAll();
    }
    
    @Test
    @DisplayName("must save a book")
    void t1() {
        // scenario
        Book book = new Book("9788550800653", "Domain Drive Design", "DDD");

        // action
        repository.save(book);

        // validation
        assertEquals(1, repository.findAll().size());
    }

    @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
        
        // alternative #1
        Throwable springException = catchException(() -> repository.save(book)); // or assertThrows() from jUnit
        assertThat(springException)
                .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")
                )
        ;

        // alternative #2 (my favorite one!)
        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")
                )
        ;

        // alternative #3
        assertThatCode(() -> { 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")
                )
        ;

        // alternative #4
        assertThatExceptionOfType(TransactionSystemException.class)
                .isThrownBy(() -> repository.save(book))
                .withRootCauseInstanceOf(ConstraintViolationException.class)
                .havingRootCause()
                .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")
                )
                ;
    }

}

Book.java

import javax.persistence.*;
import javax.validation.constraints.NotBlank;
import javax.validation.constraints.Size;

import org.hibernate.validator.constraints.ISBN;

import java.util.Objects;

import static org.hibernate.validator.constraints.ISBN.Type.ISBN_13;

@Entity
@Table(
    uniqueConstraints = {
        @UniqueConstraint(name = "uk_isbn", columnNames = "isbn")
    }
)
public class Book {

    @Id
    @GeneratedValue
    private Long id;

    @NotBlank
    @ISBN(type = ISBN_13)
    @Column(nullable = false, length = 13)
    private String isbn;

    @NotBlank
    @Size(max = 120)
    @Column(nullable = false, length = 120)
    private String title;

    @NotBlank
    @Size(max = 4000)
    @Column(nullable = false, length = 4000)
    private String description;

    /**
     * @deprecated Exclusive use of Hibernate
     */
    @Deprecated
    public Book() {}

    public Book(String isbn, String title, String description) {
        this.isbn = isbn;
        this.title = title;
        this.description = description;
    }

    public Long getId() {
        return id;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Book book = (Book) o;
        return Objects.equals(isbn, book.isbn);
    }

    @Override
    public int hashCode() {
        return Objects.hash(isbn);
    }

    @Override
    public String toString() {
        return "Book{" +
                "id=" + id +
                ", isbn='" + isbn + '\'' +
                ", title='" + title + '\'' +
                ", description='" + description + '\'' +
                '}';
    }
}

BookRepository.java

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;
import org.springframework.transaction.annotation.Transactional;

@Repository
@Transactional(readOnly = true)
public interface BookRepository extends JpaRepository<Book, Long> {

}