Injecting Autowired private field during testing

Question

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

User · Answer

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.

User · Answer

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

User · Answer

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  Kullaniciadi veya sifre hatali             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

User · Answer

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

User · Answer

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  quot magic quot  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

User · Answer

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

[java] Injecting @Autowired private field during testing

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