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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?

JUnit5: make multiple tests operate on the same object

I want to set up my JUnit5 tests to all operate on the same object. I read large files to use as test data, so I would prefer to read it once and utilize that same data for the rest of the tests.
I've created the following as a simple example where I try to achieve this using a static object ("list") (does not work):
import java.util.List;
import java.util.ArrayList;
import static org.junit.jupiter.api.Assertions.*;
import org.junit.jupiter.api.BeforeAll;
import org.junit.jupiter.api.Test;
class ExampleTest {
// Single list object to be modified and accessed by the tests
private static List<String> list = new ArrayList<String>();
#BeforeAll
static void setUpBeforeClass() throws Exception {
// None
}
#Test
final void addFoo() {
list.add("foo");
}
#Test
final void addBar() {
list.add("bar");
}
#Test
final void printList() {
System.out.println(list.toString());
assert(list.toString().equals("[foo, bar]"));
}
}
The result of this is a failure of printList() where the list is empty instead of containing [foo, bar].
I have been able to make this work is by moving the methods that add data into the #BeforeAll:
private static List<String> list;
#BeforeAll
static void setUpBeforeClass() throws Exception {
list = new ArrayList<String>();
list.add("foo");
list.add("bar");
}
But having the data importing methods as tests separate from #BeforeAll would be preferred.
#TestInstance(TestInstance.Lifecycle.PER_CLASS) did not work either.

Use #FixMethodOrder annotation.
Refer to this article for example : https://www.mkyong.com/unittest/junit-run-test-in-a-particular-order/

The issue was with the JUnit method ordering (as noted by Abhijay). Utilizing #TestMethodOrder as described in the JUnit5 documentation to appropriately order the tests gave the desired result:
import java.util.ArrayList;
import java.util.List;
import org.junit.jupiter.api.BeforeAll;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.Order;
import org.junit.jupiter.api.TestMethodOrder;
import org.junit.jupiter.api.MethodOrderer;
#TestMethodOrder(MethodOrderer.OrderAnnotation.class)
class ScratchTest {
private static List<String> list = new ArrayList<String>();
#BeforeAll
static void setUpBeforeClass() throws Exception {
// None
}
#Test
#Order(1)
final void addFoo() {
list.add("foo");
}
#Test
#Order(2)
final void addBar() {
list.add("bar");
}
#Test
#Order(3)
final void printList() {
System.out.println(list.toString());
System.out.println(list.toString().equals("[foo, bar]"));
assert(list.toString().equals("[foo, bar]"));
}
}

Pass a parameter to dataProvide when using the #Factory TestNG

There is an exception Using TestNG's #Factory and #dataProvider annotations it is not possible to pass the calling test name, this needed when building a generic test as a framework to provide different data each time(from Excel). Using Method getName() at the Dataprovider cause run time Exception. The getName() function is working when using #dataprovider only. However combined with #Factory the exception occurs. Is there a ways to solve or bypass this issue?
package Tests;
import java.lang.reflect.Method;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import org.testng.ITestContext;
import org.testng.annotations.DataProvider;
import org.testng.annotations.Test;
public abstract class GenericFactory11 {
protected List<String> data;
public GenericFactory11(List<String> data) {
this.data = data;
}
#DataProvider(name = "getDataForInstances")
public static Object[][] getDataForInstances(ITestContext context,Method m){
System.out.println(context.getName());
System.out.println(m.getName()); // THIS Line Causes the exception
return new Object[][]{
{Collections.singletonList("Java")},
{Arrays.asList("TestNG", "JUnit")},
{Arrays.asList("Maven", "Gradle", "Ant")}
};
}
}
package Tests;
import static org.testng.Assert.assertNotEquals;
import java.util.List;
import org.testng.annotations.Factory;
import org.testng.annotations.Test;
public class Sanity11 extends GenericFactory11 {
#Factory (dataProvider = "getDataForInstances")
public Sanity11(List<String> data) {
super(data);
}
#Test
public void Sanity(){
String text = this.data.get(this.data.size()-1);
System.out.println("Printing Parameters when running test method [" + text + "]");
assertNotEquals(text,"");
}
}
Running the code the following error is received:
java.lang.RuntimeException: java.lang.NullPointerException
at org.testng.internal.MethodInvocationHelper.invokeMethodNoCheckedException(MethodInvocationHelper.java:49)

You are seeing a NullPointerException because your data provider states it would be accepting a java.lang.reflect.Method object, but in this case, the calling method is a java.lang.reflect.Constructor and not a Method object.
You should be replacing java.lang.reflect.Method with org.testng.ITestNGMethod.
Here's how your modified data provider looks like:
#DataProvider(name = "getDataForInstances")
public static Object[][] getDataForInstances(ITestContext context, ITestNGMethod method) {
System.out.println("test name = " + context.getName());
System.out.println("Method name = " + method.getConstructorOrMethod().getName() + "()\n");
return new Object[][] {
{Collections.singletonList("Java")},
{Arrays.asList("TestNG", "JUnit")},
{Arrays.asList("Maven", "Gradle", "Ant")}
};
}

Passing arrays to Parameterized JUnit

I am new to parameterized feature of JUnit 4.x and having a problem. My parameterized test consists of 3 integer arrays and I am having difficulty of how to declare them. What I have below generates run-time error:
testGeneral[0] caused an ERROR: argument type mismatch
argument type mismatch
java.lang.IllegalArgumentException
at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
testGeneral[1] caused an ERROR: argument type mismatch
argument type mismatch
java.lang.IllegalArgumentException
at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
Here is my code:
#RunWith(Parameterized.class)
public class MyArrayTest {
private Integer[] inputList1;
private Integer[] inputList2;
private Integer[] expectedList;
public MyArrayTest(Integer[] li1, Integer[] li2, Integer[] expected) {
// ========> Runtime error happens here. <=========
this.inputList1 = li1;
this.inputList2 = li2;
this.expectedList = expected;
}
#Parameterized.Parameters
public static Collection testCases() {
return Arrays.asList(new Object[][][] {
{{1,1,1}, {2,2,2}, {3,3,3}},
{{2,2,2}, {3,3,3}, {4,4,4}}
});
}
#Test
public void testGeneral() {
// Do some test with this.inputList1, this.inputList2,
// and verify with this.expectedList
// I am not even getting here yet.
}
}
I appreciate your help to correctly passing the three arrays to my tests.

The reason why it is failing is because your test expects Integer arrays whereas you are passing Object type. So you are expanding the type. Try this:
#Parameterized.Parameters
public static Collection testCases() {
return Arrays.asList(new Integer[][][] {
{{1,1,1}, {2,2,2}, {3,3,3}},
{{2,2,2}, {3,3,3}, {4,4,4}}
});
}

This solution uses junitparams, implements junitparams.converters.Converter and parses list of long values as parameters.
package example;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.util.Arrays;
import java.util.stream.Collectors;
import org.junit.Test;
import org.junit.runner.RunWith;
import junitparams.JUnitParamsRunner;
import junitparams.Parameters;
import junitparams.converters.ConversionFailedException;
import junitparams.converters.Converter;
import junitparams.converters.Param;
#RunWith(JUnitParamsRunner.class)
public class LongArrayParameterTest {
#Parameters({ "0|10", "1|10;20;30" })
#Test
public void test(final long otherParameter, #LongArrayParam final long[] expected) {
System.out.println(Arrays.stream(expected).boxed().map(l -> Long.toString(l)).collect(Collectors.toList()));
}
#Retention(RetentionPolicy.RUNTIME)
#Target(ElementType.PARAMETER)
#Param(converter = LongArrayConverter.class)
public #interface LongArrayParam {
}
public static class LongArrayConverter implements Converter<LongArrayParam, long[]> {
#Override
public void initialize(final LongArrayParam annotation) {
}
#Override
public long[] convert(final Object param) throws ConversionFailedException {
final String str = (String) param;
final String[] longStrings = str.split(";");
return Arrays.stream(longStrings).mapToLong(s -> Long.parseLong(s)).toArray();
}
}
}
This parser does not support empty list.

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.