Mock a method which manipulates an input parameter

[Bill Comer]

I am trying to mock a database Dao call that saves an object in to a DB. 

The Dao calls returns the new PK, but also modifies the passed object by updating the PK.

My test is working as I want except the verify fails saying I am not passing the expected object. yet when I pause in the debugger I can see that the insert is indeed accepting an object with no PK. It is then modifying it & the calling controller can see the changed object. 

I have tried running the code with the additional commented out lines (in an attempt to know that the verify() is using an unmodified object) replacing the verify() but that also fails 

Any thoughts please ?

@Test
public void insertSampleAnalyteLabConfig() throws Exception {
   int newInt = 99;

   SampleAnalyteLabConfig sampleAnalyteLabConfig = createMockSampleAnalyteLabConfig(null);
   //SampleAnalyteLabConfig sampleAnalyteLabConfig2 = createMockSampleAnalyteLabConfig(null);

   //assertEquals("at this point they should be the same", sampleAnalyteLabConfig, sampleAnalyteLabConfig2);

   when(sampleAnalyteLabConfigService.save(sampleAnalyteLabConfig)).thenAnswer( invocation -> {
            SampleAnalyteLabConfig foo = (SampleAnalyteLabConfig) invocation.getArguments()[0];
            foo.setId(newInt);
            return new Long(newInt);
         }
   );

   mockMvc.perform(post("/api/lab/sampleanalytelab")
         .contentType(MediaType.APPLICATION_JSON_UTF8)
         .content(getBytes(sampleAnalyteLabConfig))).andExpect(status().isCreated());

   //verify(sampleAnalyteLabConfigService, times(1)).save(sampleAnalyteLabConfig2);
   verify(sampleAnalyteLabConfigService, times(1)).save(sampleAnalyteLabConfig);
}

With the code as above I get the following:

Argument(s) are different! Wanted:

sampleAnalyteLabConfigService.save(

    SampleAnalyteLabConfig{{id=0}sampleId=2, analyteId=3, labId=1, numberOfRounds=null, absolutePerformanceScoreWarning=null}

);

-> at com.lgc.controllers.LabControllerTest.insertSampleAnalyteLabConfig(LabControllerTest.java:240)

Actual invocation has different arguments:

sampleAnalyteLabConfigService.save(

    SampleAnalyteLabConfig{{id=99}sampleId=2, analyteId=3, labId=1, numberOfRounds=null, absolutePerformanceScoreWarning=null}

);

-> at com.lgc.controllers.LabController.saveSampleAnalyteLabConfig(LabController.java:165)

Comparison Failure:  <Click to see difference>

Argument(s) are different! Wanted:

sampleAnalyteLabConfigService.save(

    SampleAnalyteLabConfig{{id=0}sampleId=2, analyteId=3, labId=1, numberOfRounds=null, absolutePerformanceScoreWarning=null}

);

-> at com.lgc.controllers.LabControllerTest.insertSampleAnalyteLabConfig(LabControllerTest.java:240)

Actual invocation has different arguments:

sampleAnalyteLabConfigService.save(

    SampleAnalyteLabConfig{{id=99}sampleId=2, analyteId=3, labId=1, numberOfRounds=null, absolutePerformanceScoreWarning=null}

);

-> at com.foo.controllers.LabController.saveSampleAnalyteLabConfig(LabController.java:165)

[Malte Finsterwalder]

Hi Bill,

I'm not sure I can help. I don't have enough information. But some questions that come to my mind:

- What does getBytes(sampleAnalyteLabConfig) do? Is there some serialization involved, before the object is passed to the location, where save() is called in the code?

- Mockito probably saves the object that was passed to save() and stores it somewhere for later verify. But inside your Answer-code, you change this object. What does this do to the "to be verified"-Object?

Greetings,

   Malte

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[Bill Comer]

Malte,

Yes getBytes sderializes the object:

private byte[] getBytes(SampleAnalyteLabConfig sdDao) throws JsonProcessingException {
   ObjectMapper mapper = new ObjectMapper();
   return mapper.writeValueAsBytes(sdDao);
}

 

[Jige Yu]

I normally use @Spy to implement side-effects or to enforce invariants:

@Spy private MockSampleAnalyteService sampleAnalyteService;

@Test

public void insertSampleAnalyteLabConfig() throws Exception {
   int newInt = 99;

   SampleAnalyteLabConfig sampleAnalyteLabConfig = createMockSampleAnalyteLabConfig(null);
   //SampleAnalyteLabConfig sampleAnalyteLabConfig2 = createMockSampleAnalyteLabConfig(null);

   //assertEquals("at this point they should be the same", sampleAnalyteLabConfig, sampleAnalyteLabConfig2);

mockMvc.perform(post("/api/lab/sampleanalytelab")
         .contentType(MediaType.APPLICATION_JSON_UTF8)
         .content(getBytes(sampleAnalyteLabConfig))).andExpect(status().isCreated());

   //verify(sampleAnalyteLabConfigService, times(1)).save(sampleAnalyteLabConfig2);

   verify(sampleAnalyteLabConfigService, times(1)).saved(sampleAnalyteLabConfig);
}

abstract static class MockSampleAnalyteService implements SampleAnalyteService {
  @Override public long save(Config config) {
    config.setId(newInt);
    saved(config);
    return newInt;
  }

  abstract void saved(Config config);
}

(The blue-colored code are critical)

Using @Spy separates side-effect/invariants from interaction verification. The normal save() method does the former, and the abstract saved() method does the latter.

Although, I kinda wonder the point of doing the side-effect inside the Answer. I can understand if the subject-under-test does side-effects. But why do you need to set the id from a mock, especially if it makes testing harder?