How to write JUnit Test for uploading Image in Amazon S3 in Spring Boot

I have a problem about writing a test to upload Image in Amazon s3 in Spring Boot.

I tried to write its test method but I got an error shown below.

How can I fix it?

Here is the method of Rest controller

@RestController
@RequestMapping("/api/v1/bookImage")
@RequiredArgsConstructor
public class ImageRestController {

@PostMapping
public ResponseEntity<String> uploadImage(@RequestParam("bookId") Long bookId, @RequestParam("file") MultipartFile file) {
    final String uploadImg = imageStoreService.uploadImg(convert(file), bookId);
    service.saveImage(bookId, uploadImg);
    return ResponseEntity.ok(uploadImg);
}

private File convert(final MultipartFile multipartFile) {
   // convert multipartFile to File
   File file = new File(Objects.requireNonNull(multipartFile.getOriginalFilename()));
   try (FileOutputStream fos = new FileOutputStream(file)) {
       fos.write(multipartFile.getBytes());
       return file;
   } catch (IOException e) {
      throw new RuntimeException("Failed to convert multipartFile to File");
   }
}

Here is the method of imageService.

public String uploadImg(File file, Long bookId) {
   s3amazon.putObject(BUCKET_NAME, bookId.toString(), file);
   return baseUrl + bookId;
}

Here is the test method shown below.

@Test
    void itShouldGetImagePath_WhenValidBookIdAndFile() throws Exception{

        // given - precondition or setup
        String bookId = "1";
        String imagePath = "amazon-imagepath";
        String baseUrl = String.format(imagePath + "/%s", bookId);

        Long bookIdValue = 1L;

        MockMultipartFile uploadFile = new MockMultipartFile("file", new byte[1]);


        // when -  action or the behaviour that we are going test
        when(imageStoreService.uploadImg(convert(uploadFile), bookIdValue)).thenReturn(baseUrl); -> HERE IS THE ERROR

        // then - verify the output
        mvc.perform(MockMvcRequestBuilders.multipart("/api/v1/bookImage")
                        .file(uploadFile)
                        .param("bookId", bookId))
                .andExpect((ResultMatcher) content().string(baseUrl))
                .andExpect(status().isOk());

    }

    private File convert(final MultipartFile multipartFile) {
        // convert multipartFile to File
        File file = new File(Objects.requireNonNull(multipartFile.getOriginalFilename()));
        try (FileOutputStream fos = new FileOutputStream(file)) {
            fos.write(multipartFile.getBytes());
            return file;
        } catch (IOException e) {
            throw new RuntimeException("Failed to convert multipartFile to File");
        }
    }

Here is the error : Failed to convert multipartFile to File (java.lang.RuntimeException: Failed to convert multipartFile to Filejava.io.FileNotFoundException: )

How can I fix it?

Answer

Here is the solution shown below.

@Test
    void itShouldGetImagePath_WhenValidBookIdAndFile() throws Exception{

        // given - precondition or setup
        String bookId = "1";
        String imagePath = "amazon-imagepath";
        String baseUrl = String.format(imagePath + "/%s", bookId);

        Long bookIdValue = 1L;

        String fileName = "sample.png";
        MockMultipartFile uploadFile =
                new MockMultipartFile("file", fileName, "image/png", "Some bytes".getBytes());

        // when -  action or the behaviour that we are going test
        when(imageStoreService.uploadImg(convert(uploadFile), bookIdValue)).thenReturn(baseUrl);
        doNothing().when(bookSaveService).saveImage(bookIdValue,baseUrl);

        // then - verify the output
        mvc.perform(MockMvcRequestBuilders.multipart("/api/v1/bookImage")
                        .file(uploadFile)
                        .param("bookId", bookId))
                .andDo(print())
                .andExpect(status().isOk())
                .andExpect(jsonPath("$").value(baseUrl))
                .andExpect(content().string(baseUrl));

    }