How to test the read data from S3 bucket in spring boot application

[vishalbiradar]

How can I validate the read files functionality in the spring boot application?
I want to test it with 100% code coverage.
Can anyone help me in doing so?

Spring Boot Version: 2.3.4.RELEASE
Java Version: 8
aws-java-sdk-s3: 1.11.637
mockito: 3.3.3

S3 Read Code

	public Map<String, InputStream> readFiles(String bucketName, Collection<String> paths)
			throws Exception {
		Map<String, InputStream> s3Filesdata = new HashMap<String, InputStream>();
		try {
			for (Iterator<String> i = paths.iterator(); i.hasNext();) {
				String path = (String) i.next();
				S3Object s3Obj = getAWSS3Client().getObject(bucketName, path);
				InputStream resultInputStream = s3Obj.getObjectContent();
				s3Filesdata.put(path, resultInputStream);
			}
		} catch (SdkClientException ex) {
			throw new Exception(ex);
		}
		return s3Filesdata;
	}

	@Override
	public AmazonS3 getAWSS3Client() throws Exception {
		AmazonS3 amazonS3 = null;
		try {
			Regions s3Region = retrieveAWSRegion();
			amazonS3 = AmazonS3ClientBuilder.standard()
					.withCredentials(new AWSStaticCredentialsProvider(
							new BasicSessionCredentials(awsAccessKeyId, awsSecretAccessKey, awsSessionToken)))
					.withRegion(s3Region).build();
		} catch (Exception ex) {
			throw new Exception(ex);
		}
		return amazonS3;
	}

	private Regions retrieveAWSRegion() throws Exception {
		Regions awsRegion = null;
		try {
			if (!isValidString(awsS3Region)) {
				throw new Exception(NOT_NULL_AWS_S3_REGION);
			} else {
				awsRegion = Regions.fromName(awsS3Region);
			}
		} catch (Exception ex) {
			throw new Exception(ex);
		}
		return awsRegion;
	}

Test Code

Tried with mockito but unable to get the code coverage when I use @mock annotation but when I use @SPY and @Injectmocks annotation on service I can get the code coverage but the test is failing.

@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT, classes = MySpringBootMain.class)
@RunWith(SpringJUnit4ClassRunner.class)
public class ControllerTest {

	private String bucketName = "bucket_name";
	String s3FilePath = "some_file_path";
	private List<String> s3FilePathList = Arrays.asList(s3FilePath);

	@Spy
	@InjectMocks
	private MyService servicce = new MyServiceImpl(
			"src/test/resources/aws_credentials.json", bucketName, "us-west-2");

	@Mock
	AmazonS3 mockS3Client;

	@Test
	public void myTest() {
		Map<String, InputStream> mockResults = new HashMap<String, InputStream>();
		InputStream inputStream = new ByteArrayInputStream("content".getBytes());
		MyService.put(s3FilePath, inputStream);

		when(service.getAWSS3Client()).thenReturn(mockS3Client);

		S3Object obj = mock(S3Object.class);

		when(obj.getObjectContent()).thenReturn(new S3ObjectInputStream(inputStream, null));

		when(mockS3Client.getObject(bucketName, s3FilePath)).thenReturn(obj);

		when(service.readFiles(bucketName, s3FilePathList)).thenReturn(MyService);

		Map<String, InputStream> actualResults = service.readFiles(bucketName,
				s3FilePathList);

		assertThat(actualResults).isEqualTo(MyService);
	}
}

Error

when I use @SPY and @Injectmocks annotation on the service I can get the code coverage but the test is failing.

org.mockito.exceptions.misusing.WrongTypeOfReturnValue: 
HashMap cannot be returned by getObjectContent()
getObjectContent() should return S3ObjectInputStream