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Test fails on a null pointer exception when I use #InjectMocks

I am practising restful api endpoints using https://api.predic8.de/shop/docs
Here is my repo
I am getting a NPE failure when I try to use #InjectMocks during my TDD approach
However, I can make my test pass when I make a direct call in the setup()
vendorService = new VendorServiceImpl(VendorMapper.INSTANCE, vendorRepository);
I wanted to extend my learning by trying to create an endpoint for getting all vendors.
When I employ TDD along the way, but, my test getAllVendors() fails on a NPE when I try to use #InjectMocks but passes when I substitute it for a direct call in the setup() method.
The NPE is linked to the mapper class I think.
Here are the classes that I believe are useful. VendorServiceTest, VendorServiceImpl, VendorMapper.
I have commented out the direct call in the setup as I want to get the test passing using #InjectMocks
package guru.springfamework.services;
import guru.springfamework.api.v1.mapper.VendorMapper; import
guru.springfamework.api.v1.model.VendorDTO; import
guru.springfamework.domain.Vendor; import
guru.springfamework.repositories.VendorRepository; import
org.junit.Before; import org.junit.Test; import
org.mockito.InjectMocks; import org.mockito.Mock; import
org.mockito.MockitoAnnotations; import
org.springframework.test.web.servlet.MockMvc;
import java.util.Arrays; import java.util.List;
import static org.junit.Assert.*; import static
org.mockito.Mockito.when;
public class VendorServiceTest {
public static final String NAME = "Tasty";
public static final Long ID = 1L;
#Mock
VendorMapper vendorMapper;
#Mock
VendorRepository vendorRepository;
#InjectMocks
VendorServiceImpl vendorService;
//VendorService vendorService;
#Before
public void setUp() throws Exception {
MockitoAnnotations.initMocks(this);
//vendorService = new VendorServiceImpl(VendorMapper.INSTANCE, vendorRepository);
}
#Test
public void getAllVendors() {
//given
List<Vendor> vendors = Arrays.asList(new Vendor(), new Vendor(), new Vendor());
when(vendorRepository.findAll()).thenReturn(vendors);
//when
List<VendorDTO> vendorDTOList = vendorService.getAllVendors();
//then
assertEquals(3, vendorDTOList.size());
}
#Test
public void findByName() {
}
}
package guru.springfamework.services;
import guru.springfamework.api.v1.mapper.VendorMapper; import
guru.springfamework.api.v1.model.VendorDTO; import
guru.springfamework.repositories.VendorRepository; import
org.springframework.stereotype.Service;
import java.util.List; import java.util.stream.Collectors;
#Service public class VendorServiceImpl implements VendorService {
private final VendorMapper vendorMapper;
private final VendorRepository vendorRepository;
public VendorServiceImpl(VendorMapper vendorMapper, VendorRepository vendorRepository) {
this.vendorMapper = vendorMapper;
this.vendorRepository = vendorRepository;
}
#Override
public List<VendorDTO> getAllVendors() {
return vendorRepository
.findAll()
.stream()
.map(vendor -> {
VendorDTO vendorDTO = vendorMapper.vendorToVendorDTO(vendor);
vendorDTO.setVendorUrl("/api/v1/vendors/" + vendor.getId());
return vendorDTO;
})
.collect(Collectors.toList());
}
#Override
public VendorDTO findByName(String name) {
return vendorMapper.vendorToVendorDTO(vendorRepository.findByName(name));
}
#Override
public VendorDTO getVendorById(Long id) {
return vendorMapper.vendorToVendorDTO(vendorRepository.findById(id).orElseThrow(RuntimeException::new));
}
}
package guru.springfamework.api.v1.mapper;
import guru.springfamework.api.v1.model.VendorDTO; import
guru.springfamework.domain.Vendor; import org.mapstruct.Mapper; import
org.mapstruct.factory.Mappers;
#Mapper public interface VendorMapper {
VendorMapper INSTANCE = Mappers.getMapper(VendorMapper.class);
VendorDTO vendorToVendorDTO(Vendor vendor);
}
Does anyone know where and why I am going wrong?

The problem is that you created mock object for the mapper, but you didn't say what should happen when the method vendorToVendorDTO is called.
Therefore, when that method is called in the next line of code:
VendorDTO vendorDTO = vendorMapper.vendorToVendorDTO(vendor);
It will return null, and then in this line of code:
vendorDTO.setVendorUrl("/api/v1/vendors/" + vendor.getId());
You will get NullPointerException.
To make this work, change your getAllVendors() method as follows:
#Test
public void getAllVendors() {
//given
List<Vendor> vendors = Arrays.asList(new Vendor(), new Vendor(), new Vendor());
VendorDTO mockDto = mock(VendorDTO.class);
when(vendorRepository.findAll()).thenReturn(vendors);
when(vendorMapper.vendorToVendorDTO(any(Vendor.class))).thenReturn(mockDto);
//when
List<VendorDTO> vendorDTOList = vendorService.getAllVendors();
//then
assertEquals(3, vendorDTOList.size());
}
And the test should pass.

Have you tried to put #RunWith(MockitoJUnitRunner.class)/#ExtendsWith(MockitoExtension.class) over your test class?

Mokito/Java - Static Methods Mock

For example I have the following classes below:
public class TesteEstatico {
public static String teste(){
return "FOO";
}
}
And I have a class that uses her method:
public class UsaTesteEstatico {
public String metodoParaTeste1 (){
return TesteEstatico.teste() + " BAR ";
}
public String metodoParaTeste2 (){
return "FOO "+TesteEstatico.teste() + " BAR ";
}
}
Test class:
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.mockito.InjectMocks;
import org.mockito.Mockito;
import org.mockito.junit.jupiter.MockitoExtension;
#ExtendWith(MockitoExtension.class) public class UsaTesteEstaticoTest {
#InjectMocks
UsaTesteEstatico usaTesteEstatico;
#Test
void teste1(){
Mockito.mockStatic(TesteEstatico.class);
Mockito.when(TesteEstatico.teste())
.thenReturn("BANANA");
String res = usaTesteEstatico.metodoParaTeste1();
System.out.println(res);
}
#Test
void teste2(){
Mockito.mockStatic(TesteEstatico.class);
Mockito.when(TesteEstatico.teste())
.thenReturn("LARANJA");
String res = usaTesteEstatico.metodoParaTeste2();
System.out.println(res);
}
}
Error I get when trying to run the tests:
org.mockito.exceptions.base.MockitoException:
For TesteEstatico, static mocking is already registered in the current thread
To create a new mock, the existing static mock registration must be deregistered
Versions of the libs that are in the project:
junit-jupiter 5.5.2
mockito-junit-jupiter 3.2.14
mockito-inline 3.2.14
Any idea how to solve this, i've tried a few things but nothing successful.
NOTE: I cannot change or add any new libraries as it is a restricted project.

You should use try-with-resources block in each of the tests to close the mockStatic.
public class UsaTesteEstaticoTest {
UsaTesteEstatico usaTesteEstatico = new UsaTesteEstatico();
#Test
void teste1(){
try (var ms = Mockito.mockStatic(TesteEstatico.class)) {
Mockito.when(TesteEstatico.teste()).thenReturn("BANANA");
String res = usaTesteEstatico.metodoParaTeste1();
System.out.println(res);
}
}
#Test
void teste2(){
try (var ms = Mockito.mockStatic(TesteEstatico.class)) {
Mockito.when(TesteEstatico.teste()).thenReturn("LARANJA");
String res = usaTesteEstatico.metodoParaTeste2();
System.out.println(res);
}
}
}
Note on mockStatic in #BeforeAll
Using #BeforeAll is a trap and bad advice.
You should strive for independent tests that don't affect each other.
This is not the case for mockStatic called in #BeforeAll, as stubbing from test methods outlive the test methods.
For example
// BAD CODE DONT USE
public class UsaTesteEstaticoTest {
UsaTesteEstatico usaTesteEstatico = new UsaTesteEstatico();
static MockedStatic<TesteEstatico> ms;
#BeforeAll
public static void init() {
ms = Mockito.mockStatic(TesteEstatico.class);
}
#AfterAll
public static void close() {
ms.close();
}
#Test
void teste1() {
Mockito.when(TesteEstatico.teste()).thenReturn("BANANA");
String res = usaTesteEstatico.metodoParaTeste1();
System.out.println(res);
}
#Test
void teste2() {
String res = usaTesteEstatico.metodoParaTeste2();
System.out.println(res);
}
}
teste2 prints:
FOO BANANA BAR if run after teste1
FOO null BAR if run separately
This is precisely what you want to avoid.

you need to use static block to mock it.
import org.junit.jupiter.api.AfterAll;
import org.junit.jupiter.api.BeforeAll;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.mockito.InjectMocks;
import org.mockito.Mockito;
import org.mockito.junit.jupiter.MockitoExtension;
#ExtendWith(MockitoExtension.class)
public class UsaTesteEstaticoTest {
#InjectMocks
UsaTesteEstatico usaTesteEstatico;
#BeforeAll
public static void init(){
Mockito.mockStatic(TesteEstatico.class);
}
#Test
void teste1(){
Mockito.when(TesteEstatico.teste())
.thenReturn("BANANA");
String res = usaTesteEstatico.metodoParaTeste1();
System.out.println(res);
}
#Test
void teste2(){
Mockito.when(TesteEstatico.teste())
.thenReturn("LARANJA");
String res = usaTesteEstatico.metodoParaTeste2();
System.out.println(res);
}
}

Mock actorRef.tell inside an Actor class

I have an actor class EmployeeActor, inside that actor, some other actor is fired using payrollRunActor.tell(). I need to write a JUnit test for EmployeeActor.java, but I don't want to fire payrollRunActor.tell(), means I want to mock it.
Is there a way to do it? I tried a lot, but real payrollRunActor is getting fired.
Here is the actual code of my EmployeeActor class.
package com.test.periodic.actors;
import java.util.List;
import org.apache.commons.lang3.RandomStringUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import com.test.avs.domain.boundedcontext.Employee;
import com.test.avs.domain.boundedcontext.PayrollRun;
import com.test.entity.BusinessDTO;
import com.test.periodic.actors.aggregrators.EmployeeAggregator;
import akka.actor.AbstractActor;
import akka.actor.ActorRef;
import akka.actor.ActorSystem;
import akka.actor.Props;
import akka.routing.RoundRobinPool;
public class EmployeeActor extends AbstractActor {
private static final Logger logger = LoggerFactory.getLogger(EmployeeActor.class);
private boolean rollup;
public static Props props() {
return Props.create(EmployeeActorTest.class);
}
private List<PayrollRun> payrollRuns;
private String instanceId;
private String employeeAggregatorId;
private Employee employee;
private ActorRef organizationAggregatorActor;
private List<BusinessDTO> businessDTOs;
final ActorSystem payrollRunSystem = ActorSystem.create("payrollRun");
ActorRef employeeAggregator;
public EmployeeActor(ActorRef organizationAggregatorActor, List<PayrollRun> payrollRuns,
Employee employee, List<BusinessDTO> businessDTOs, boolean rollup) {
this.payrollRuns = payrollRuns;
this.employee = employee;
this.organizationAggregatorActor = organizationAggregatorActor;
this.businessDTOs = businessDTOs;
this.rollup = rollup;
}
#Override
public void preStart() throws Exception {
instanceId = RandomStringUtils.randomAlphanumeric(6);
employeeAggregatorId = "employeeAggregator-" + instanceId;
employeeAggregator = getContext().system().actorOf(
Props.create(EmployeeAggregator.class, organizationAggregatorActor, employee),
employeeAggregatorId);
super.preStart();
}
#Override
public Receive createReceive() {
return receiveBuilder().match(Employee.class, employee -> {
if (rollup) {
logger.info("Rollingup business entities.");
employeeAggregator.tell(employee, getSelf());
} else {
ActorRef payrollRunActor = payrollRunSystem.actorOf(new RoundRobinPool(payrollRuns.size())
.props(Props.create(PayrollRunActor.class, employeeAggregator, employee, businessDTOs)));
for (PayrollRun payrollRun : payrollRuns) {
**payrollRunActor.tell(payrollRun, getSelf());**
}
}
}).match(PayrollRun.class, maxPaydatePayrollRun -> {
ActorRef payrollRunActor = payrollRunSystem
.actorOf(Props.create(PayrollRunActor.class, employeeAggregator, employee, businessDTOs));
**payrollRunActor.tell(maxPaydatePayrollRun, getSelf());**
}).build();
}
}

First of all you would have to mock the static method call which is invoked during the creation of class under test. Then make it return a spied object and mock the method you want to avoid calling:
#RunWith(PowerMockRunner.class)
#PrepareForTest(ActorSystem.class)
public void TestClass{
#Test
public void test(){
// Arrange
PowerMockito.mockStatic(ActorSystem.class);
ActorSystem actorSystemMock = Mockito.mock(ActorSystem.class);
Actor actorSpy = Mockito.spy(new Actor());
Mockito.when(ActorSystem.create("payrollRun")).thenReturn(actorSystemSpy);
Mockito.when(actorSystemMock.actorOf(any(RoundRobinPool.class)))
.thenReturn(actorSpy);
Mockito.doNothing().when(actorSpy)
.tell(Mockito.any(PayrollRun.class), Mockito.any(Self.class));
EmployeeActor employeeActor = new EmployeeActor();
// Act and assert...
employeeActor.createReceive();
}
}
Remember that all other methods of actorSystemSpy will be called will real implementation. If you want to mock all of them then use Mockito.mock instead of spy.

mocking consecutive REST call

I have a service/dao layer. Service layer method calls 1st method of dao from which I get response and call the second method in dao passing some arguments including the value from the response of 1st dao method. I tried using mock but its failing with null pointer.
pseudo code is something like below:
Service{
serviceMethod(some_args){
response1 = dao.method1(some_args);
someItem = response1.get("someItem");
/* do some logic on someitem to create otherItem*/
request2.setArgs(someItem);
response2 = dao.method2(request2);
}
}
I have tried to mock as below but its not working.
#Test
public void testPass(){
mockResponse1 = new Response1();
mockRequest2 = new MockRequest2();
when(dao.method1(some_args)).thenReturn(mockResponse1)
mockResponse1.setArgs(some_args);
mockRequest2.setArgs(mockResponse1.getargs());
mockResponse2 = new Response2();
when(dao.method2(mockRequest2)).thenReturn(mockResponse2)
service.serviceMethod(some_args)
}

You could use an ArgumentCaptor to get the value that was passed into dao.method2(...) and then make assertions on that.
For example, say I had this DAO...
public interface DAO {
Response method1(Request request);
Response method2(Request request);
}
And this service...
public class Service {
private DAO dao;
public void setDao(DAO dao) {
this.dao = dao;
}
public Response serviceMethod(Request someArgs) {
Response response1 = dao.method1(someArgs);
String someItem = response1.getTheResponse();
Request request2 = new Request(someItem);
return dao.method2(request2);
}
}
A test for this service could be...
import static org.fest.assertions.Assertions.assertThat;
import static org.mockito.Matchers.any;
import static org.mockito.Mockito.verify;
import static org.mockito.Mockito.when;
import org.junit.Before;
import org.junit.Test;
import org.mockito.ArgumentCaptor;
import org.mockito.Captor;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.MockitoAnnotations;
public class ServiceTest {
#Mock
private Request request;
#Mock
private Response response;
#Mock
private Response serviceResponse;
#Mock
private DAO dao;
#InjectMocks
private Service service;
#Captor
private ArgumentCaptor<Request> requestCaptor;
#Before
public void setup() {
MockitoAnnotations.initMocks(this);
}
#Test
public void shouldDoServiceMethod() {
// Set up
when(dao.method1(request)).thenReturn(response);
when(response.getTheResponse()).thenReturn("[ARGUMENT]");
when(dao.method2(any(Request.class))).thenReturn(serviceResponse);
// Code under test
Response actualResponse = service.serviceMethod(request);
// Verification
assertThat(actualResponse).isSameAs(serviceResponse);
verify(dao).method2(requestCaptor.capture());
Request actualSecondRequest = requestCaptor.getValue();
assertThat(actualSecondRequest.getArgs()).isEqualTo("[ARGUMENT]");
}
}
The key line being...
verify(dao).method2(requestCaptor.capture());
This verifies that method2 was called and captures the value that it was called with.
You then get the value...
Request actualSecondRequest = requestCaptor.getValue();
...and you can then verify that the relevant information was set...
assertThat(actualSecondRequest.getArgs()).isEqualTo("[ARGUMENT]");
Hope this helps.
For completeness, here's Request and Response...
public class Request {
private String args;
public Request(String args) {
this.args = args;
}
public String getArgs() {
return args;
}
}
public class Response {
private String theResponse;
public Response(String theResponse) {
this.theResponse = theResponse;
}
public String getTheResponse() {
return theResponse;
}
}

Is it possible to use partial mocking for private static methods in PowerMock?

From the examples on the PowerMock homepage, I see the following example for partially mocking a private method with Mockito:
#RunWith(PowerMockRunner.class)
// We prepare PartialMockClass for test because it's final or we need to mock private or static methods
#PrepareForTest(PartialMockClass.class)
public class YourTestCase {
#Test
public void privatePartialMockingWithPowerMock() {
PartialMockClass classUnderTest = PowerMockito.spy(new PartialMockClass());
// use PowerMockito to set up your expectation
PowerMockito.doReturn(value).when(classUnderTest, "methodToMock", "parameter1");
// execute your test
classUnderTest.execute();
// Use PowerMockito.verify() to verify result
PowerMockito.verifyPrivate(classUnderTest, times(2)).invoke("methodToMock", "parameter1");
}
However, this approach does not seem to work when the private method we wish to mock is static. I wish to create a partial mock of the below class, with the readFile method mocked:
package org.rich.powermockexample;
import java.io.File;
import java.io.IOException;
import java.nio.charset.Charset;
import java.util.List;
import static com.google.common.io.Files.readLines;
public class DataProvider {
public static List<String> getData() {
List<String> data = null;
try {
data = readFile();
} catch (IOException e) {
e.printStackTrace();
}
return data;
}
private static List<String> readFile() throws IOException {
File file = new File("/some/path/to/file");
List<String> lines = readLines(file, Charset.forName("utf-8"));
return lines;
}
}
Please could someone let me know how this can be achieved?

After doing a bit more research, it seems that PowerMockito.spy() and PowerMockito.doReturn() are what is required here:
package com.richashworth.powermockexample;
import org.junit.Before;
import org.junit.BeforeClass;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.powermock.api.mockito.PowerMockito;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;
import java.util.ArrayList;
import java.util.List;
import static org.junit.Assert.assertEquals;
#RunWith(PowerMockRunner.class)
#PrepareForTest({DataProvider.class})
public class ResultsWriterTest {
private static List<String> mockData = new ArrayList<String>();
private ResultsWriter resultsWriter;
#BeforeClass
public static void setUpOnce() {
final String firstLine = "Line 1";
final String secondLine = "Line 2";
mockData.add(firstLine);
mockData.add(secondLine);
}
#Before
public void setUp() {
resultsWriter = new ResultsWriter();
}
#Test
public void testGetDataAsString() throws Exception {
PowerMockito.spy(DataProvider.class);
PowerMockito.doReturn(mockData).when(DataProvider.class, "readFile");
final String expectedData = "Line 1\nLine 2\n";
final String returnedString = resultsWriter.getDataAsString();
assertEquals(expectedData, returnedString);
}
}
For further details and the complete code listing, check out my blog post here: https://richashworth.com/post/turbocharge-your-mocking-framework-with-powermock/

Test class:
#RunWith(PowerMockRunner.class)
#PrepareForTest(DataProvider.class)
public class DataProviderTest {
#Test
public void testGetDataWithMockedRead() throws Exception {
mockStaticPartial(DataProvider.class, "readFile");
Method[] methods = MemberMatcher.methods(DataProvider.class, "readFile");
expectPrivate(DataProvider.class, methods[0]).andReturn(Arrays.asList("ohai", "kthxbye"));
replay(DataProvider.class);
List<String> theData = DataProvider.getData();
assertEquals("ohai", theData.get(0));
assertEquals("kthxbye", theData.get(1));
}
}
Class being tested (basically yours):
public class DataProvider {
public static List<String> getData() {
try {
return readFile();
} catch (IOException e) {
e.printStackTrace();
return null;
}
}
private static List<String> readFile() throws IOException {
File file = new File("/some/path/to/file");
return readLines(file, Charset.forName("utf-8"));
}
}

In general, only use static mocking for classes that are beyond your control (e.g. java.io.File). Since DataProvider and readFile are your own, refactor DataProvider into a proper class (i.e. make its methods non-static), pull out readFile into a helper object and then mock that. See this answer https://stackoverflow.com/a/8819339/116509.