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// Tutorial //Mockito @InjectMocks - Mocks Dependency InjectionPublished on August 3, 2022JavaMockito![]() By Pankaj ![]() While we believe that this content benefits our community, we have not yet thoroughly reviewed it. If you have any suggestions for improvements, please let us know by clicking the “report an issue“ button at the bottom of the tutorial. Mockito @InjectMocks annotations allow us to inject mocked dependencies in the annotated class mocked object. This is useful when we have external dependencies in the class we want to mock. We can specify the mock objects to be injected using @Mock or @Spy annotations. Mockito @InjectMocksMockito tries to inject mocked dependencies using one of the three approaches, in the specified order. Constructor Based Injection - when there is a constructor defined for the class, Mockito tries to inject dependencies using the biggest constructor. Setter Methods Based - when there are no constructors defined, Mockito tries to inject dependencies using setter methods. Field Based - if there are no constructors or field-based injection possible, then mockito tries to inject dependencies into the field itself.If there is only one matching mock object, then mockito will inject that into the object. If there is more than one mocked object of the same class, then mock object name is used to inject the dependencies. Mock @InjectMocks ExampleLet’s create some services and classes with dependencies so that we can see Mockito dependency injection of mocks in action. Service Classes package com.journaldev.injectmocksservices; public interface Service { public boolean send(String msg); } package com.journaldev.injectmocksservices; public class EmailService implements Service { @Override public boolean send(String msg) { System.out.println("Sending email"); return true; } } package com.journaldev.injectmocksservices; public class SMSService implements Service { @Override public boolean send(String msg) { System.out.println("Sending SMS"); return true; } }App Service Classes with Dependencies package com.journaldev.injectmocksservices; //For Constructor Based @InjectMocks injection public class AppServices { private EmailService emailService; private SMSService smsService; public AppServices(EmailService emailService, SMSService smsService) { this.emailService = emailService; this.smsService = smsService; } public boolean sendSMS(String msg) { return smsService.send(msg); } public boolean sendEmail(String msg) { return emailService.send(msg); } } package com.journaldev.injectmocksservices; //For Property Setter Based @InjectMocks injection public class AppServices1 { private EmailService emailService; private SMSService smsService; public void setEmailService(EmailService emailService) { this.emailService = emailService; } public void setSmsService(SMSService smsService) { this.smsService = smsService; } public boolean sendSMS(String msg) { return smsService.send(msg); } public boolean sendEmail(String msg) { return emailService.send(msg); } } package com.journaldev.injectmocksservices; //For Field Based @InjectMocks injection public class AppServices2 { private EmailService emailService; private SMSService smsService; public boolean sendSMS(String msg) { return smsService.send(msg); } public boolean sendEmail(String msg) { return emailService.send(msg); } } @InjectMocks Constructor Injection Example package com.journaldev.mockito.injectmocks; import static org.junit.jupiter.api.Assertions.*; import static org.mockito.Mockito.*; import org.junit.jupiter.api.Test; import org.mockito.InjectMocks; import org.mockito.Mock; import com.journaldev.injectmocksservices.AppServices; import com.journaldev.injectmocksservices.AppServices1; import com.journaldev.injectmocksservices.AppServices2; import com.journaldev.injectmocksservices.EmailService; import com.journaldev.injectmocksservices.SMSService; class MockitoInjectMocksExamples extends BaseTestCase { @Mock EmailService emailService; @Mock SMSService smsService; @InjectMocks AppServices appServicesConstructorInjectionMock; @InjectMocks AppServices1 appServicesSetterInjectionMock; @InjectMocks AppServices2 appServicesFieldInjectionMock; @Test void test_constructor_injection_mock() { when(appServicesConstructorInjectionMock.sendEmail("Email")).thenReturn(true); when(appServicesConstructorInjectionMock.sendSMS(anyString())).thenReturn(true); assertTrue(appServicesConstructorInjectionMock.sendEmail("Email")); assertFalse(appServicesConstructorInjectionMock.sendEmail("Unstubbed Email")); assertTrue(appServicesConstructorInjectionMock.sendSMS("SMS")); } }Did you noticed that my test class is extending BaseTestCase. This is to initialize Mockito mocks before the tests, here is the code of the class. package com.journaldev.mockito.injectmocks; import org.junit.jupiter.api.BeforeEach; import org.mockito.MockitoAnnotations; class BaseTestCase { @BeforeEach void init_mocks() { MockitoAnnotations.initMocks(this); } }If you won’t call MockitoAnnotations.initMocks(this); then you will get NullPointerException. Also, I am using JUnit 5 to run the test cases. If you are not familiar with it, have a look at JUnit 5 Tutorial. @InjectMocks Setter Methods Injection Example @Test void test_setter_injection_mock() { when(appServicesSetterInjectionMock.sendEmail("New Email")).thenReturn(true); when(appServicesSetterInjectionMock.sendSMS(anyString())).thenReturn(true); assertTrue(appServicesSetterInjectionMock.sendEmail("New Email")); assertFalse(appServicesSetterInjectionMock.sendEmail("Unstubbed Email")); assertTrue(appServicesSetterInjectionMock.sendSMS("SMS")); } @InjectMocks Field Based Injection Example @Test void test_field_injection_mock() { when(appServicesFieldInjectionMock.sendEmail(anyString())).thenReturn(true); when(appServicesFieldInjectionMock.sendSMS(anyString())).thenReturn(true); assertTrue(appServicesFieldInjectionMock.sendEmail("Email")); assertTrue(appServicesFieldInjectionMock.sendEmail("New Email")); assertTrue(appServicesFieldInjectionMock.sendSMS("SMS")); }You can check out complete code and more Mockito examples from our GitHub Repository. Reference: API Doc Thanks for learning with the DigitalOcean Community. Check out our offerings for compute, storage, networking, and managed databases. Learn more about us Want to learn more? Join the DigitalOcean Community!Join our DigitalOcean community of over a million developers for free! Get help and share knowledge in our Questions & Answers section, find tutorials and tools that will help you grow as a developer and scale your project or business, and subscribe to topics of interest. Sign up nowAbout the authors![]() author Still looking for an answer?Ask a questionSearch for more helpWas this helpful? JournalDevDigitalOcean EmployeeThe sample looks confuse… mocking the class you try to test… what are you testing then? your class? no… Mockito maybe? - Domingo Berrón JournalDevDigitalOcean EmployeeWhy are you writing when(appServicesFieldInjectionMock.sendEmail(anyString())).thenReturn(true); ??? It should be when(emailService.send(anyString()) … Otherwise what is the purpose of @Mock annotated objects here. - stupid JournalDevDigitalOcean EmployeeMockito now has a JUnit5 extension to avoid having to call explicitly to initMocks(). Just adding @ExtendWith(MockitoExtension.class) At the top of the class, equivalent to the JUnit4’s @RunWith(… Dependency is: org.mockito mockito-junit-jupiter 3.5.11 test Please update the post, thanks. - brujua JournalDevDigitalOcean Employeewhere did you mock the Constructor with Arguments ??? - Bhargava Surimenu JournalDevDigitalOcean EmployeeWe should not mock the testing classes, eg: AppServices - Siva R JournalDevDigitalOcean Employeeno source code displayed - tester ![]() |
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