Spring Boot: @Autowired throws 'UnsatisfiedDependencyException' while testing

Question

Good evening,

since I'm new to Java and Spring Boot, my following question might sound easy and simple to most of you, but I would like to ask what I'm doing wrong when autowiring a model - please excuse if I'm mixing terminology of java/spring boot and python/django - inside my spring boot test.

Followed some simple steps to set up a test project:

1. Created example project with start.spring.io

   Project: Maven, Language: Java, Spring Boot 3.2.3, Java: 21

2. Created a small model class called Book.java and a repository called BookRepository.java

3. Created a placeholder test and tried to run it

Directory:

├── src
    ├── main
    │   ├── java
    │   │   ├── com.example.demo
    │   │   │   ├── book
    │   │   │   │   ├── models
    │   │   │   │   |   └── Book.java
    │   │   │   │   ├── repository
    │   │   │   │   │   └── BookRepository.java
    │   │   │   └── DemoApplication.java
    │   └── resources
    ├── test
    │   ├── java
    │   │   ├── com.example.demo
    │   │   │   ├── book
    │   │   │   │   ├── models
    │   │   │   │   │   └── BookTest.java
    ├── ...

Book.java

@Data
@AllArgsConstructor
@NoArgsConstructor
@Builder
@Entity
@Table(name = "books")
public class Book {
    @Id
    private String isbn;

    @Column(unique = true, nullable = false)
    private String title;

    @Column(nullable = false)
    private Integer pages;

    @Column(nullable = false)
    private boolean available = true;
}

BookRepository.java

public interface BookRepository extends CrudRepository<Book, String> {
}

BookTest.java

@SpringBootTest(classes = DemoApplication.class)
public class BookTest {

    @Autowired private BookRepository bookRepository;  // <-- works fine
    @Autowired private Book book;  // <-- throws error

    @Test
    @DisplayName("Placeholder")
    public void testPlaceholder() {
        System.out.println("Placeholder test get's executed!");
    }
}

Now, whenever I try to autowire the book class, the following error get's thrown when running the test:

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'com.example.demo.book.BookTest': Unsatisfied dependency expressed through field 'book': No qualifying bean of type 'com.example.demo.book.models.Book' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}

Might someone explain to me what I'm doing wrong or am i missing here? Obviously the error comes from my Book.java, but what and why do I have to add / change / remove something from there?

Thanks in advance and have a great sunday!