Java 单元测试 - 未抛出异常

Question

Trying to write a test that will call my method, when that method makes a call to another method we will throw a custom exception i have made. Here i have simplified it all

2 functions

public MyJsonResponse hello() {
        MyJsonResponse response = new MyJsonResponse();
        response.setErrorMessage("1");
        response.setStatus("some status");
        response.setData("1");
        response.setHttpResponse(200);
        try{
            hi();
            return response;
        }catch (MyServiceException e) {
            response.setErrorMessage(e.getMessage());
            response.setStatus("error creating");
            response.setData("2");
            response.setHttpResponse(e.getResponseStatus());
            return response;
        }

    }

    public String hi() throws  MyServiceException{
        LOG.error("Exception");
        return "yea";
    }

The test I have written is this

    @Test
    public void myTest() throws Exception {

        given(service.hi()).willAnswer( invocation -> { throw new MyServiceException("abc msg",511); });
        MyJsonResponse actual = service.hello();

        Assert.assertNotNull(actual);
        assertEquals(511, actual.getHttpResponse());
    }

But unfortunately the result is as follows

java.lang.AssertionError: 
Expected :511
Actual   :200

Answer 1

regarding what you explain and what your code look like, I am not sure if I have well understood. Thus, if you want that, your hi(): function throws an exception. You have to make it first throws an exception. Take a look at code below!

 public String hi() throws  MyServiceException{
        /*LOG.error("Exception");//No don't just log, throw a real exception as below*/
       throw new MyServiceException("text here, if your constructor support it or nothing otherwise")
     /*return "yea";//Nothing to return? we have just break the code by throwing the exception above*/
    }

After that, please be very sure that your 'MyServiceException.getHttpResponse()' will really return 511

Answer 2

Please, be sure that you are using a spy as you want to use the actual code for some methods of your mocked service and just stubbing specific methods of it. Please, see for instance this related SO question about the subject.

Also, consider modifying your test definition to use willThrow instead of willAnswer : as pointed out by @eis, you can still use the later, but the former is more straightforward.

Your code will look similar to this:

@Test
public void myTest() throws Exception {
  MyService service = spy(MyService.class);

  willThrow(new MyServiceException("abc msg",511))
    .given(service)
    .hi()
  ;

  // As pointed out by @eis, you can still use willAnswer
  // willAnswer(
  //   invocation -> { throw new MyServiceException("abc msg",511);}
  // )
  //   .given(service)
  //   .hi()
  // ;

  
  MyJsonResponse actual = service.hello();

  Assert.assertNotNull(actual);
  assertEquals(511, actual.getHttpResponse());
}

Answer 3

For this test to make sense, your hi() call should be done calling another service that you stub/mock in your test class. You're not doing that, so this approach won't work.

You wrote "the real method that hi represents does a lot", so it's about time you extract that to another service.