我正在使用amazons3进行文档存储。我需要为使用s3的服务类编写测试用例。
如何模拟s3对象？
我试过下面的，但得到的是NPE。
示例测试用例：

@ExtendWith(MockitoExtension.class)
class MyServiceTest {

    @InjectMocks
    private MyService myService;

    @InjectMocks
    private S3Service s3Service;
    @Mock
    private S3Configuration.S3Storage s3Storage;
    @Mock
    private AmazonS3 amazonS3;

    @BeforeEach
    public void setup() {
        ReflectionTestUtils.setField(myService, "s3Service", s3Service);
        ReflectionTestUtils.setField(s3Service, "s3Storage", s3Storage);
    }

 @Test
    void getDetailTest() {

        given(s3Storage.getClient()).willReturn(amazonS3);
        given(s3Service.getBucket()).willReturn("BUCKET1");
        given(s3Service.readFromS3(s3Service.getBucket(),"myfile1.txt")).willReturn("hello from s3 file"); //Null pointer exception
}
}

下面是抛出NPE的s3服务类示例。

public String readFromS3(String bucketName, String key) {
        var s3object = s3Storage.getClient().getObject(new GetObjectRequest(bucketName, key));
//s3Object is getting null when run the test case.
    //more logic

}

如何从MyService类模拟s3Service.readFromS3()？