How to write test cases for get image api from external url using rest assured

Question

I have a image url which will be my query parameter in the api. Here I am fetching the image by using query parameter and respond back with InputStreamResource.

Can anybody help me to write the proper test cases by using rest assured. Please find the below sample code.

Assume Sample Image URL : http://asdas.reutyure.asdas.com/AA/pet/images/cat/Test-E0173.svg

Image Controller

@GetMapping(path = "/image")
    public ResponseEntity<InputStreamResource> getImage(@RequestParam("url") String url) {

        String fileName = url.substring(url.lastIndexOf('/') + 1, url.length());
        byte[] byteContent = imageService.getImageData(url);
        InputStream resourceInputStream = new ByteArrayInputStream(byteContent);

        return ResponseEntity.ok().header("Content-disposition", "attachment; filename=" + fileName)
                .contentType(MediaType.parseMediaType("application/octet-stream")).contentLength(byteContent.length)
                .body(new InputStreamResource(resourceInputStream));

    }

Image Service

public byte[] getImageData(String url) {
        try {
            RestTemplate restTemplate = new RestTemplate();
            byte[] responseEntity = restTemplate.getForObject(url, String.class).getBytes(StandardCharsets.ISO_8859_1);
            if (responseEntity != null) {
                return responseEntity;
            }
        } catch (Exception e) {
        }
        return new byte[0];
    }

ImageResourceTest

@TestInstance(Lifecycle.PER_CLASS)
class ImageResourceTest extends BaseTest {

    private static final String IMAGE_URL_PARAMETER = "http://asdas.reutyure.asdas.com/AA/pet/images/cat/Test-E0173.svg";


    @Test
    void getImageDetails() throws Exception {
    
    // How to write proper test cases for this functionality

        given() //
                .header(authHeader()) //
                .queryParam(IMAGE_URL, IMAGE_URL_PARAMETER) //
                .when() //
                .get(contextPath + "/image") //
                .then() //
                .statusCode(200);
    }

}