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 @Override
    public byte[] downloadFile(String bucket, String fileName) throws FileDownloadException, IOException {

        JsonNode keys = getSecrets(bucket);
        String bucketId = keys.get("bucket").asText();

        final AmazonS3 s3Client = awsS3ClientBuilderService.createAwsS3Client(keys.get("api_key").asText(),
                keys.get("secret_key").asText(), Regions.US_EAST_1);

        if (bucketIsEmpty(s3Client, bucketId)) {
            this.awsS3ClientBuilderService.shutdown(s3Client);
            throw new FileDownloadException("Requested bucket does not exist or is empty");
        }
        GetObjectRequest getObjectRequest = new GetObjectRequest(bucketId, fileName);

        S3Object s3Object = s3Client.getObject(getObjectRequest);

        S3ObjectInputStream objectInputStream = s3Object.getObjectContent();

        byte[] bytes = IOUtils.toByteArray(objectInputStream);
        this.awsS3ClientBuilderService.shutdown(s3Client);
        if (bytes != null && bytes.length != 0) {
            return bytes;
        } else {
            throw new FileDownloadException("Could not find the file!");
        }
    }


private boolean bucketIsEmpty(AmazonS3 s3Client, String bucketName) {
		ListObjectsV2Result result = s3Client.listObjectsV2(bucketName);
		if (result == null) {
			return false;
		}
		List<S3ObjectSummary> objects = result.getObjectSummaries();
		return objects.isEmpty();
	}

write a unit testcase for the above downloadFile() code 
 if (bucketIsEmpty(s3Client, bucketId)) {
            this.awsS3ClientBuilderService.shutdown(s3Client);
            throw new FileDownloadException("Requested bucket does not exist or is empty");
        }
        GetObjectRequest getObjectRequest = new GetObjectRequest(bucketId, fileName);

        S3Object s3Object = s3Client.getObject(getObjectRequest);

        S3ObjectInputStream objectInputStream = s3Object.getObjectContent();

        byte[] bytes = IOUtils.toByteArray(objectInputStream);
        this.awsS3ClientBuilderService.shutdown(s3Client);
        if (bytes != null && bytes.length != 0) {
            return bytes;
        } else {
            throw new FileDownloadException("Could not find the file!");
        }
    }
it was not covered for the above lines 

@Test
    void testDownloadFile_Error() throws Exception {
        try {
            byte[] result = fileMgmtService.downloadFile(AppTestConstants.BUCKET, AppTestConstants.FILENAME);
        } catch (Exception e) {
            Assertions.assertEquals(AppTestConstants.DOWNLOAD_FILE_ERROR_STR, e.getMessage());
        }
    }

this is the previous code