无法为包含更新方法的RestController执行Junit测试用例？

Question

在尝试为包含 update 方法的 controller 类编写 Junit Test 案例时，遇到错误了吗？

我已经为其他方法编写了 JUnit 测试用例，但是当我尝试为 update 方法运行junit测试用例时，出现了以下错误。 org.junit.ComparisonFailure：预期：<“ [{” title“：”使用JPA休眠“，”主题“：” Java“，”发布者“：” IGH出版物“，”语言“：”英语“， “ numberOfPages”：1532，“ isbn”：“ EMP_6953_2019”}]“>但为：<” []“>

LibraryController.java

@PutMapping("/books/{isbn}")
    public ResponseEntity<Book> updateBook(@PathVariable String isbn, @Valid @RequestBody Book bookDetails) {
        log.info("Entering updateBook() method ");
        Book updatedBook = librarianService.updateBook(isbn, bookDetails);
        log.info("Exiting updateBook() method ");
        return ResponseEntity.ok(updatedBook);
    }

updateBook（）方法的Junit测试用例。
LibraryControllerTest.java

@Test
    public void testUpdateBook() throws Exception {

        Book book1 = new Book("EMP_6953_2019", "Hibernate", "Java", "IGH Pubications", "English", 1232);
        String isbn = book1.getISBN();
        Book bookDetails = new Book("EMP_6953_2019", "Hibernate with JPA", "Java", "IGH Pubications", "English", 1532);
        when(librarianService.updateBook(isbn, bookDetails)).thenReturn(bookDetails);

        MockHttpServletResponse response = mockMvc.perform(put("/librarian/books/{isbn}", "EMP_6953_2019")
                .contentType(MediaType.APPLICATION_JSON).content(jsonList.write(bookDetails).getJson())).andReturn()
                .getResponse();
        assertThat(response.getStatus()).isEqualTo(HttpStatus.OK.value());
        assertThat(response.getContentAsString()).isEqualTo(jsonList
                .write(new Book(bookDetails.getISBN(), bookDetails.getTitle(), bookDetails.getSubject(),
                        bookDetails.getPublisher(), bookDetails.getLanguage(), bookDetails.getNumberOfPages()))
                .getJson());

    }

预期输出：
“ {” title“：” Hibernate with JPA“，” subject“：” Java“，” publisher“：” IGH Pubications“，” language“：” English“，” numberOfPages“：1532，” isbn“：” EMP_6953_2019“ }”
实际输出：
“”