Add code from article (#10552)

spring-boot-modules/spring-boot-data-2/src/test/java/com/baeldung/boot/readonlyrepository/BookRepository.java

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+package com.baeldung.boot.readonlyrepository;
+
+import org.springframework.data.repository.CrudRepository;
+
+public interface BookRepository extends BookReadOnlyRepository, CrudRepository<Book, Long> {
+}

spring-boot-modules/spring-boot-data-2/src/test/java/com/baeldung/boot/readonlyrepository/ReadOnlyRepositoryUnitTest.java

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+package com.baeldung.boot.readonlyrepository;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+
+import java.util.List;
+import java.util.NoSuchElementException;
+
+@SpringBootTest( classes = ReadOnlyRepositoryApplication.class )
+public class ReadOnlyRepositoryUnitTest
+{
+    @Autowired
+    private BookRepository bookRepository;
+
+    @Autowired
+    private BookReadOnlyRepository bookReadOnlyRepository;
+
+    @Test
+    public void givenBooks_whenUsingReadOnlyRepository_thenGetThem() {
+        Book aChristmasCarolCharlesDickens = new Book();
+        aChristmasCarolCharlesDickens.setTitle("A Christmas Carol");
+        aChristmasCarolCharlesDickens.setAuthor("Charles Dickens");
+        bookRepository.save(aChristmasCarolCharlesDickens);
+
+        Book greatExpectationsCharlesDickens = new Book();
+        greatExpectationsCharlesDickens.setTitle("Great Expectations");
+        greatExpectationsCharlesDickens.setAuthor("Charles Dickens");
+        bookRepository.save(greatExpectationsCharlesDickens);
+
+        Book greatExpectationsKathyAcker = new Book();
+        greatExpectationsKathyAcker.setTitle("Great Expectations");
+        greatExpectationsKathyAcker.setAuthor("Kathy Acker");
+        bookRepository.save(greatExpectationsKathyAcker);
+
+        List<Book> charlesDickensBooks = bookReadOnlyRepository.findByAuthor("Charles Dickens");
+        Assertions.assertEquals(2, charlesDickensBooks.size());
+
+        List<Book> greatExpectationsBooks = bookReadOnlyRepository.findByTitle("Great Expectations");
+        Assertions.assertEquals(2, greatExpectationsBooks.size());
+
+        List<Book> allBooks = bookReadOnlyRepository.findAll();
+        Assertions.assertEquals(3, allBooks.size());
+
+        Long bookId = allBooks.get(0).getId();
+        Book book = bookReadOnlyRepository.findById(bookId).orElseThrow(NoSuchElementException::new);
+        Assertions.assertNotNull(book);
+    }
+}