这是我的密码：

public String getDate() throws IOException {
    StringBuilder fileURI = new StringBuilder(locationName);
    fileURI.append(fileName);
    S3ObjectInputStream ts = null;
    ts = (S3ObjectInputStream) s3Services.getResourceStream(fileURI.toString());
    String timeStamp;
    String onlyDate = null;
    LocalDate mydate;
    try (BufferedReader reader = new BufferedReader(new InputStreamReader(ts))) {
        timeStamp = reader.readLine();
        onlyDate = timeStamp.substring(0, 10);
        LocalDate date = LocalDate.parse(onlyDate);
        mydate= date.minusDays(1);

    }
    return mydate.toString();
}

我第一次在junit上工作。
我需要模拟S3服务并测试是否使用预期值调用了getresourcestream（）。
我试图模拟s3objectinputstream，并确保调用了其上的正确方法。

@Test
public void testgetDate() throws IOException {
Mockito.mock(Service.class);
StringBuilder fileURI = new StringBuilder("test");
fileURI.append("testFile.txt");
Mockito.mock(S3ObjectInputStream .class);
S3ObjectInputStream ts = null;
Mockito.when(s3Services.getResourceStream(fileURI.toString())).thenReturn(ts);
service.getDate();

}