如何使用 Mockito Junit 5 为 lambda 表达式创建 Junit 测试用例？

Question

I want to create Junit TestCases of method, in which we are iterating List<Map<String,Object>> using forEach loop with lambda expresion. Now I want to mock statement objectMapper.writeValueAsString(recordObj.get("value")); but I am not understanding how to use recordObj .

public String apply(MyRequestWrapper requestWrapper) {
        String resultStr=null;
        final Map<String, List<PubSubEvent>> packagesEventList = AppUtilities.getPackagesEventsMappedList();

        try {
            logger.debug("Received Record:: " + requestWrapper.getBody().toString());
            List<RecordProcessedResult> results = new ArrayList<>();
            List<Map<String,Object>> recordMaps= string2List(objectMapper,requestWrapper.getBody().toString());
            logger.debug("Parsed received payload ::: "+ LocalDateTime.now() + " batch size is ::: "+ recordMaps.size());
            
            
            if(! ObjectUtils.isEmpty(recordMaps) && !recordMaps.isEmpty() ) {
                recordMaps.forEach(recordObj ->{
                    ConsumerRecord record=objectMapper.convertValue(recordObj, ConsumerRecord.class);
                    String topicName = recordObj.get("topic").toString();
                    String key = null;
                    String value = null;
                    String offset = null;
                    String xTraceabilityId = ((Map<String, String>) recordObj.get("headers")).get(IdTypeConstants.XTRACEABILITYID);
                    String xCorrelationId = ((Map<String, String>) recordObj.get("headers")).get(IdTypeConstants.XCORRELATIONID);
                    
                    MDC.put(IdTypeConstants.XTRACEABILITYID, xTraceabilityId);
                    MDC.put(IdTypeConstants.XCORRELATIONID, xCorrelationId);
                    
                    try {
                        key = objectMapper.writeValueAsString(recordObj.get("key"));
                        value = objectMapper.writeValueAsString(recordObj.get("value"));
                        offset = objectMapper.writeValueAsString(recordObj.get("offset"));
                    
                        MyEvent myEvent= objectMapper.readValue(value, MyEvent.class);

                        subscribedPackageProcessor.setInput(input);
                        subscribedPackageProcessor.setOutput(output);
                        subscribedPackageProcessor.setPackagesEventList(packagesEventList);
                        subscribedPackageProcessor.setRequesterType(requesterType);                subscribedPackageProcessor.processSubscribedPackage(myEvent.getPackageId());
                        RecordProcessedResult rpr = new RecordProcessedResult(record, true, null, xTraceabilityId, xCorrelationId, key, System.currentTimeMillis());
                        results.add(rpr);
                    }
                    catch(Exception e) {
                        RecordProcessedResult rpr = new RecordProcessedResult(record, false, ExceptionUtils.getStackTrace(e), xTraceabilityId, xCorrelationId, key, System.currentTimeMillis());
                        results.add(rpr);
                        logger.info("Exception occured while processing fund data :::out  ", e);
                    }
                    MDC.clear();

                });
            }
            resultStr = objectMapper.writeValueAsString(results);
        }catch (Exception e) {
            logger.debug(e.getMessage());
        }
        return resultStr;
    }

I have tried following testcases.

@Test void applyTest() throws Exception { 
        MyEvent myEvent = new MyEvent(); 
        myEvent.setPackageId("test"); 
        MyRequestWrapper flowRequestWrapper= getMyRequestWrapper();
        List<Map<String, Object>> maps = string2List(objectMapper1, flowRequestWrapper.getBody().toString());
        Map<String,Object> map = new HashMap<String, Object>();
        Mockito.when(objectMapper.readValue(Mockito.anyString(), Mockito.any(TypeReference.class))).thenReturn(maps);
        Mockito.when(objectMapper.writeValueAsString(Mockito.anyString())).thenReturn("test");
        Mockito.when(objectMapper.readValue(Mockito.anyString(), Mockito.eq(MyEvent.class))).thenReturn(myEvent);
        //doNothing().when(subscribedPackageProcessor).processSubscribedPackage("");
        String response = processESignCompletedEventSvcFlow.apply(flowRequestWrapper);
        Assertions.assertNotNull(response); 
    }

Please help, Thanks

Answer 1

Your method is way too complex to be unit tested. For example it declares dependencies by calling methods in the same class. You cannot mock those and it makes the testing many times more complicated.

List<Map<String,Object>> recordMaps =
    string2List(objectMapper,requestWrapper.getBody().toString());

You need to extract the string2List method into a standalone class (with it's own unit tests) that is injected into your class as a dependency.

Then you can just mock the string2List class and when you do that, you control the creation of recordObj instances from your unit test for this method.

Your second "sin" is abusing lambdas by creating one that is longer than two lines. Lambdas should be short. If it spans more than a few lines, it must be extracted into a standalone class that can be unit tested separately. And again, when you have extracted this lambda into a standalone class and unit tested it, you can't just go " new RecordObjConsumer(results) " in your method, as that creates a hard-coded dependency that you again cannot mock. You need to design the consumer so that it can be injected into your class as an external dependency.