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Spring injecting an initiallized mock via constructor

I have a singleton class (so private constructor) which needs to use a Spring Data repository during initialization. I have one injected as a constructor argument. Roughly:
#Controller
public class MyClass {
#Autowired
private MyClass(MyRepository repo) {
repo.findAll();
}
}
I want to unit test my class, so I need to have a mock repository initialized with mock values and then passed into my class before my class is initialized. How do I write my Mockito mocks in my JUnit test to make this possible?

You don't need Spring; this is an advantage of constructor injection. Just use MyRepository mockRepo = mock(MyRepository.class) and new MyClass(mockRepo).
(Your constructor should be public, by the way. You seem to be making the common mistake of confusing different senses of "singleton"; in the case of DI it simply means that the container only makes a single instance and shares it. Finally, if you only have one constructor you don't need #Autowired.)

Unit test should be independent. It means, we are not using real data from database even call any service from our test file.
Assuming you are using JUni5 and have findAllStudents() in your controller. So your test file approximately like this
#TestInstance(TestInstance.Lifecycle.PER_CLASS)
public class MyClassTest {
#Mock
private MyRepository repo;
#InjectMocks
private MyClass controller;
#BeforeAll
public void setup() {
MockitoAnnotations.initMocks(this);
}
#Test
public void testDataIsExist() {
List<String> expectednames = new ArrayList();
expectedNames.add("Foo");
expectedNames.add("Bar");
Mockito.when(myRepo.findAll()).thenReturn(expectedNames);
List<String> result = controller.findAllStudents();
Assertions.assertNotNull(result);
Assertions.assertEquals(expectednames, result);
}
}
So we are mock all the services we use in controller, then inject to controller itself. Then inside the test method we mock repo.findAll() to return expectedNames so if the controller find that function it will return what mock says to return.
After we call the function, we have to make it sure that the result is according to what we expected.

There is little value in a "unit test" for a #Controller implementation. If you use #WebMvcTest, then you can use #MockBean:
#WebMvcTest
class MyControllerTest {
#Autowired
private MockMvc mockMvc;
#MockBean
private MyRepository repository;
#Test
void testSomething() {
mockMvc.perform( ... );
}
}

Unit test of Spring boot service with private fields and #PostConstruct

I have a Spring boot service defined like this
#Service
public class MyService {
private String field1;
private String field2;
#Autowired
private AnotherService anotherService
#PostConstruct
public void init() {
anotherService.initField1(field1);
anotherService.initField2(field2);
}
public String foo() {
return field1 + field2;
}
}
How should I write a unit test for foo. Well, it's more about how to deal with class fields and the PostConstruct methods.
Thanks!!
EDIT:
Added AnotherService as a field as well.

The following example shows a #Service Bean that uses constructor injection to obtain a required AnotherService bean:
#Service
public class MyService {
private String field1;
private String field2;
private final AnotherService anotherService;
public MyService(AnotherService anotherService) {
this.anotherService = anotherService;
this.anotherService.initField1(field1);
this.anotherService.initField2(field2);
}
public String foo() {
return field1 + field2;
}
}
Note you can omit the #Autowired becuase MyService has one constructor. See here for more info.
testing with Spring
Use the #RunWith(SpringRunner.class) and #SpringBootTest to inject MyService and start using it:
#RunWith(SpringRunner.class)
#SpringBootTest
public class MyServiceTest {
#Autowired
private MyService service;
#Test
public void testFoo() {
String expResult = "";
String result = service.foo();
assertEquals(expResult, result);
}
}
testing without Spring
public class MyServiceTest2 {
private MyService service;
#Before
public void setUp() {
service = new MyService(new AnotherService.Fake());
}
#Test
public void testFoo() {
String expResult = "";
String result = service.foo();
assertEquals(expResult, result);
}
}
Here Fake is a fake implementation of the AnotherService interface which allows you to have a pure unit test.

Writing good, testable code can be hard. There are some pitfalls waiting for everyone to fall into sooner or later.
As a rule of thumb, try to avoid field level injection, use constructor parameter injection instead:
#Service
public class MyService {
private AnotherService anotherService;
#Autowired
MyService (AnotherService anotherService) {
this.anotherService = anotherService;
}
}
This is the cleanest solution. You can call the constructor from your tests, spring will inject dependencies the same way at runtime. So there is no difference to deal with.
The same goes for any life cycle constructs like #PostConstruct. If you can avoid them, do it. Let the constructor handle it. If you absolutely have to keep them around, well, the only logical solution is to manually call them from your test code.
Now, how to setup services that at runtime would be autowired by the container?
For unit testing, you basically have three options (in no particular order):
If the required service is rather simple and can easily be constructed, create and pass it as the framework would do.
If the service has a limited interface that does not change too often, create a fake service.
Use a mocking lib like mockito (spring-boot-test provides it by default).

Injecting a String property with #InjectMocks

I have a Spring MVC #Controller with this constructor:
#Autowired
public AbcController(XyzService xyzService, #Value("${my.property}") String myProperty) {/*...*/}
I want to write a standalone unit test for this Controller:
#RunWith(MockitoJUnitRunner.class)
public class AbcControllerTest {
#Mock
private XyzService mockXyzService;
private String myProperty = "my property value";
#InjectMocks
private AbcController controllerUnderTest;
/* tests */
}
Is there any way to get #InjectMocks to inject my String property? I know I can't mock a String since it's immutable, but can I just inject a normal String here?
#InjectMocks injects a null by default in this case. #Mock understandably throws an exception if I put it on myProperty. Is there another annotation I've missed that just means "inject this exact object rather than a Mock of it"?

You can't do this with Mockito, but Apache Commons actually has a way to do this using one of its built in utilities. You can put this in a function in JUnit that is run after Mockito injects the rest of the mocks but before your test cases run, like this:
#InjectMocks
MyClass myClass;
#Before
public void before() throws Exception {
FieldUtils.writeField(myClass, "fieldName", fieldValue, true);
}

Since you're using Spring, you can use the org.springframework.test.util.ReflectionTestUtils from the spring-test module. It neatly wraps setting a field on a object or a static field on a class (along with other utility methods).
#RunWith(MockitoJUnitRunner.class)
public class AbcControllerTest {
#Mock
private XyzService mockXyzService;
#InjectMocks
private AbcController controllerUnderTest;
#Before
public void setUp() {
ReflectionTestUtils.setField(controllerUnderTest, "myProperty",
"String you want to inject");
}
/* tests */
}

You cannot do this with Mockito, because, as you mentioned yourself, a String is final and cannot be mocked.
There is a #Spy annotation which works on real objects, but it has the same limitations as #Mock, thus you cannot spy on a String.
There is no annotation to tell Mockito to just inject that value without doing any mocking or spying. It would be a good feature, though. Perhaps suggest it at the Mockito Github repository.
You will have to manually instantiate your controller if you don't want to change your code.
The only way to have a pure annotation based test is to refactor the controller. It can use a custom object that just contains that one property, or perhaps a configuration class with multiple properties.
#Component
public class MyProperty {
#Value("${my.property}")
private String myProperty;
...
}
This can be injected into the controller.
#Autowired
public AbcController(XyzService xyzService, MyProperty myProperty) {
...
}
You can mock and inject this then.
#RunWith(MockitoJUnitRunner.class)
public class AbcControllerTest {
#Mock
private XyzService mockXyzService;
#Mock
private MyProperty myProperty;
#InjectMocks
private AbcController controllerUnderTest;
#Before
public void setUp(){
when(myProperty.get()).thenReturn("my property value");
}
/* tests */
}
This is not pretty straight forward, but at least you will be able to have a pure annotation based test with a little bit of stubbing.

Just don't use #InjectMocks in that case.
do:
#Before
public void setup() {
controllerUnderTest = new AbcController(mockXyzService, "my property value");
}

Solution is simple: You should put constructor injection for the object type while for primitive/final dependencies you can simply use setter injection and that'll be fine for this scenario.
So this:
public AbcController(XyzService xyzService, #Value("${my.property}") String myProperty) {/*...*/}
Would be changed to:
#Autowired
public AbcController(XyzService xyzService) {/*...*/}
#Autowired
public setMyProperty(#Value("${my.property}") String myProperty){/*...*/}
And the #Mock injections in test would be as simple as:
#Mock
private XyzService xyzService;
#InjectMocks
private AbcController abcController;
#BeforeMethod
public void setup(){
MockitoAnnotations.initMocks(this);
abcController.setMyProperty("new property");
}
And that'll be enough. Going for Reflections is not advisable!
PLEASE AVOID THE USAGE OF REFLECTIONS IN PRODUCTION CODE AS MUCH AS POSSIBLE!!
For the solution of Jan Groot I must remind you that it will become very nasty since you will have to remove all the #Mock and even #InjectMocks and would have to initialize and then inject them manually which for 2 dependencies sound easy but for 7 dependencies the code becomes a nightmare (see below).
private XyzService xyzService;
private AbcController abcController;
#BeforeMethod
public void setup(){ // NIGHTMARE WHEN MORE DEPENDENCIES ARE MOCKED!
xyzService = Mockito.mock(XyzService.class);
abcController = new AbcController(xyzService, "new property");
}

What you can use is this :
org.mockito.internal.util.reflection.Whitebox
Refactor your "AbcController" class constructor
In your Test class "before" method, use Whitebox.setInternalState method to specify whatever string you want
#Before
public void setUp(){
Whitebox.setInternalState(controllerUnderTest, "myProperty", "The string that you want"); }

If you want to have no change in your code then use ReflectionTestUtils.setField method
How do I mock an autowired #Value field in Spring with Mockito?

Injecting #Autowired private field during testing

I have a component setup that is essentially a launcher for an application. It is configured like so:
#Component
public class MyLauncher {
#Autowired
MyService myService;
//other methods
}
MyService is annotated with the #Service Spring annotation and is autowired into my launcher class without any issues.
I would like to write some jUnit test cases for MyLauncher, to do so I started a class like this:
public class MyLauncherTest
private MyLauncher myLauncher = new MyLauncher();
#Test
public void someTest() {
}
}
Can I create a Mock object for MyService and inject it into myLauncher in my test class? I currently don't have a getter or setter in myLauncher as Spring is handling the autowiring. If possible, I'd like to not have to add getters and setters. Can I tell the test case to inject a mock object into the autowired variable using an #Before init method?
If I'm going about this completely wrong, feel free to say that. I'm still new to this. My main goal is to just have some Java code or annotation that puts a mock object in that #Autowired variable without me having to write a setter method or having to use an applicationContext-test.xml file. I would much rather maintain everything for the test cases in the .java file instead of having to maintain a separate application content just for my tests.
I am hoping to use Mockito for the mock objects. In the past I have done this by using org.mockito.Mockito and creating my objects with Mockito.mock(MyClass.class).

You can absolutely inject mocks on MyLauncher in your test. I am sure if you show what mocking framework you are using someone would be quick to provide an answer. With mockito I would look into using #RunWith(MockitoJUnitRunner.class) and using annotations for myLauncher. It would look something like what is below.
#RunWith(MockitoJUnitRunner.class)
public class MyLauncherTest
#InjectMocks
private MyLauncher myLauncher = new MyLauncher();
#Mock
private MyService myService;
#Test
public void someTest() {
}
}

The accepted answer (use MockitoJUnitRunner and #InjectMocks) is great. But if you want something a little more lightweight (no special JUnit runner), and less "magical" (more transparent) especially for occasional use, you could just set the private fields directly using introspection.
If you use Spring, you already have a utility class for this : org.springframework.test.util.ReflectionTestUtils
The use is quite straightforward :
ReflectionTestUtils.setField(myLauncher, "myService", myService);
The first argument is your target bean, the second is the name of the (usually private) field, and the last is the value to inject.
If you don't use Spring, it is quite trivial to implement such a utility method. Here is the code I used before I found this Spring class :
public static void setPrivateField(Object target, String fieldName, Object value){
try{
Field privateField = target.getClass().getDeclaredField(fieldName);
privateField.setAccessible(true);
privateField.set(target, value);
}catch(Exception e){
throw new RuntimeException(e);
}
}

Sometimes you can refactor your #Component to use constructor or setter based injection to setup your testcase (you can and still rely on #Autowired). Now, you can create your test entirely without a mocking framework by implementing test stubs instead (e.g. Martin Fowler's MailServiceStub):
#Component
public class MyLauncher {
private MyService myService;
#Autowired
MyLauncher(MyService myService) {
this.myService = myService;
}
// other methods
}
public class MyServiceStub implements MyService {
// ...
}
public class MyLauncherTest
private MyLauncher myLauncher;
private MyServiceStub myServiceStub;
#Before
public void setUp() {
myServiceStub = new MyServiceStub();
myLauncher = new MyLauncher(myServiceStub);
}
#Test
public void someTest() {
}
}
This technique especially useful if the test and the class under test is located in the same package because then you can use the default, package-private access modifier to prevent other classes from accessing it. Note that you can still have your production code in src/main/java but your tests in src/main/test directories.
If you like Mockito then you will appreciate the MockitoJUnitRunner. It allows you to do "magic" things like #Manuel showed you:
#RunWith(MockitoJUnitRunner.class)
public class MyLauncherTest
#InjectMocks
private MyLauncher myLauncher; // no need to call the constructor
#Mock
private MyService myService;
#Test
public void someTest() {
}
}
Alternatively, you can use the default JUnit runner and call the MockitoAnnotations.initMocks() in a setUp() method to let Mockito initialize the annotated values. You can find more information in the javadoc of #InjectMocks and in a blog post that I have written.

I believe in order to have auto-wiring work on your MyLauncher class (for myService), you will need to let Spring initialize it instead of calling the constructor, by auto-wiring myLauncher. Once that is being auto-wired (and myService is also getting auto-wired), Spring (1.4.0 and up) provides a #MockBean annotation you can put in your test. This will replace a matching single beans in context with a mock of that type. You can then further define what mocking you want, in a #Before method.
public class MyLauncherTest
#MockBean
private MyService myService;
#Autowired
private MyLauncher myLauncher;
#Before
private void setupMockBean() {
doNothing().when(myService).someVoidMethod();
doReturn("Some Value").when(myService).someStringMethod();
}
#Test
public void someTest() {
myLauncher.doSomething();
}
}
Your MyLauncher class can then remain unmodified, and your MyService bean will be a mock whose methods return values as you defined:
#Component
public class MyLauncher {
#Autowired
MyService myService;
public void doSomething() {
myService.someVoidMethod();
myService.someMethodThatCallsSomeStringMethod();
}
//other methods
}
A couple advantages of this over other methods mentioned is that:
You don't need to manually inject myService.
You don't need use the Mockito runner or rules.

I'm a new user for Spring. I found a different solution for this. Using reflection and making public necessary fields and assign mock objects.
This is my auth controller and it has some Autowired private properties.
#RestController
public class AuthController {
#Autowired
private UsersDAOInterface usersDao;
#Autowired
private TokensDAOInterface tokensDao;
#RequestMapping(path = "/auth/getToken", method = RequestMethod.POST)
public #ResponseBody Object getToken(#RequestParam String username,
#RequestParam String password) {
User user = usersDao.getLoginUser(username, password);
if (user == null)
return new ErrorResult("Kullanıcıadı veya şifre hatalı");
Token token = new Token();
token.setTokenId("aergaerg");
token.setUserId(1);
token.setInsertDatetime(new Date());
return token;
}
}
And this is my Junit test for AuthController. I'm making public needed private properties and assign mock objects to them and rock :)
public class AuthControllerTest {
#Test
public void getToken() {
try {
UsersDAO mockUsersDao = mock(UsersDAO.class);
TokensDAO mockTokensDao = mock(TokensDAO.class);
User dummyUser = new User();
dummyUser.setId(10);
dummyUser.setUsername("nixarsoft");
dummyUser.setTopId(0);
when(mockUsersDao.getLoginUser(Matchers.anyString(), Matchers.anyString())) //
.thenReturn(dummyUser);
AuthController ctrl = new AuthController();
Field usersDaoField = ctrl.getClass().getDeclaredField("usersDao");
usersDaoField.setAccessible(true);
usersDaoField.set(ctrl, mockUsersDao);
Field tokensDaoField = ctrl.getClass().getDeclaredField("tokensDao");
tokensDaoField.setAccessible(true);
tokensDaoField.set(ctrl, mockTokensDao);
Token t = (Token) ctrl.getToken("test", "aergaeg");
Assert.assertNotNull(t);
} catch (Exception ex) {
System.out.println(ex);
}
}
}
I don't know advantages and disadvantages for this way but this is working. This technic has a little bit more code but these codes can be seperated by different methods etc. There are more good answers for this question but I want to point to different solution. Sorry for my bad english. Have a good java to everybody :)

Look at this link
Then write your test case as
#RunWith(SpringJUnit4ClassRunner.class)
#ContextConfiguration({"/applicationContext.xml"})
public class MyLauncherTest{
#Resource
private MyLauncher myLauncher ;
#Test
public void someTest() {
//test code
}
}

How to mock a private dao variable?

I have a dao.create() call that I want to mock when testing a method.
But I am missing something as I'm still getting NPE. What is wrong here?
class MyService {
#Inject
private Dao dao;
public void myMethod() {
//..
dao.create(object);
//
}
}
How can I mock out the dao.create() call?
#RunWith(PowerMockRunner.class)
#PrepareForTest(DAO.class)
public void MyServiceTest {
#Test
public void testMyMethod() {
PowerMockito.mock(DAO.class);
MyService service = new MyService();
service.myMethod(); //NPE for dao.create()
}
}

You are not injecting the DAO. With mockito you can change your test class to use #InjectMocks and use mockito runner.
#RunWith(MockitoJUnitRunner.class)
public void MyServiceTest {
#Mock
private Dao dao;
#InjectMocks
private MyService myService;
...
}
You can read more about InjectMocks at Inject Mocks API
Simpler way is changing your injection to injection by constructor. For example, you would change MyService to
class MyService {
...
private final Dao dao;
#Inject
public MyService(Dao dao) {
this.dao = dao;
}
...
}
then your test you could simple pass the mocked DAO in setup.
...
#Mock
private Dao dao;
#Before
public void setUp() {
this.dao = mock(Dao.class);
this.service = new MyService(dao);
}
...
now you can use verify to check if create was called, like:
...
verify(dao).create(argThat(isExpectedObjectBeingCreated(object)));
}
private Matcher<?> isExpectedObjectBeingCreated(Object object) { ... }
Using injection by constructor will let your dependencies clearer to other developers and it will help when creating tests :)

You still need to set the dao field with your mock.
You can use reflection to this.

You need to inject/set the mocked object DAO in your service class.
If it is a spring based project, you may have a look # Spring Junit Testrunner

If you use new MyService() the Dao is never injected. For the Dao to be injected you need to load the MyService via an ApplicationContext (Spring) or an Injector (Guice). Like you would in your normal application.

As others have already said, you need to set the dao field in your MyService class in some fashion. I'm unsure the mechanism to allow for a compound runner on your test to use both Powermock and a DI framework runner (assuming Powermock is required), but as long as you're already using PowerMock (for reasons unclear in the given example), you could avail yourself of the Whitebox class to set the dao more manually.
public void testMyMethod() {
Dao dao = mock(Dao.class)
doNothing().when(dao).create(anyObject())); //assuming no return val for dao.create()
MyService service = new MyService();
Whitebox.setInternalState(service, "dao", dao);
service.myMethod();
}