Mockito dependency setup in JUnit - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Mockito used for in testing?

Mockito is a Java library used to create mock objects for unit testing. It helps simulate behavior of real objects to test code in isolation.

beginner

How do you add Mockito dependency using Maven?

Add this to your pom.xml inside <dependencies>:

<dependency>
  <groupId>org.mockito</groupId>
  <artifactId>mockito-core</artifactId>
  <version>5.4.0</version>
  <scope>test</scope>
</dependency>

beginner

How to add Mockito dependency using Gradle?

Add this line to your build.gradle inside dependencies:

testImplementation 'org.mockito:mockito-core:5.4.0'

intermediate

What JUnit version is commonly used with Mockito 5+?

JUnit 5 (JUnit Jupiter) is commonly used with Mockito 5 and above for modern testing features and better integration.

intermediate

What is the purpose of the @ExtendWith(MockitoExtension.class) annotation?

It tells JUnit 5 to enable Mockito support, so you can use annotations like @Mock and @InjectMocks without manual setup.

Which Maven scope should you use for Mockito dependency?

A test

B compile

C provided

D runtime

Mockito is used only during testing, so the 'test' scope ensures it is not included in production builds.

Which Gradle configuration is correct for adding Mockito?

A implementation 'org.mockito:mockito-core:5.4.0'

B compileOnly 'org.mockito:mockito-core:5.4.0'

C runtimeOnly 'org.mockito:mockito-core:5.4.0'

D testImplementation 'org.mockito:mockito-core:5.4.0'

Mockito is a test library, so it should be added with 'testImplementation' to be available only during tests.

What annotation enables Mockito support in JUnit 5?

A @RunWith(MockitoJUnitRunner.class)

B @MockitoTest

C @ExtendWith(MockitoExtension.class)

D @MockSupport

In JUnit 5, '@ExtendWith(MockitoExtension.class)' activates Mockito features like mocks and injections.

Which version of Mockito is recommended for use with JUnit 5?

A 5.x

B 2.x

C 3.x

D 1.x

Mockito 5.x is the latest major version with improved support for JUnit 5.

Why do we use mock objects in unit testing?

A To test the real database

B To simulate dependencies and isolate the unit under test

C To slow down tests

D To replace the entire application

Mocks simulate dependencies so tests focus only on the code being tested, making tests faster and more reliable.

Explain how to set up Mockito dependency in a Java project using Maven or Gradle.

Think about where to add dependencies in build files and the scope for test libraries.

Describe the role of the @ExtendWith(MockitoExtension.class) annotation in JUnit 5 tests.

Consider how JUnit 5 integrates with Mockito to simplify test setup.

Practice

1. What is the main purpose of setting up Mockito as a dependency in a JUnit project?

easy

A. To automatically generate user interfaces

B. To create fake objects for testing without using real implementations

C. To improve the performance of the application in production

D. To deploy the application to a server

Solution

1. Step 1: Understand Mockito's role

   Mockito is a tool used to create mock objects that simulate real objects in tests.

2. Step 2: Identify the purpose in testing

   Using mocks helps isolate the code under test by replacing dependencies with fake versions.

3. Final Answer:

   To create fake objects for testing without using real implementations -> Option B

4. Quick Check:

   Mockito = mock objects for testing [OK]

Hint: Mockito creates fake objects to test code easily [OK]

Common Mistakes:

• Thinking Mockito improves production performance
• Confusing Mockito with UI tools
• Assuming Mockito deploys applications

2. Which of the following is the correct Maven dependency snippet to add Mockito version 4.11.0 for test scope?

easy

A.
org.mockito
mockito-core
4.11.0
test

B.
org.mockito
mockito-core
4.11.0

C.
org.mockito
mockito-all
3.0.0
compile

D.
org.mockito
mockito-core
5.0.0
test

Solution

1. Step 1: Check groupId and artifactId

   The correct groupId is 'org.mockito' and artifactId is 'mockito-core' for Mockito library.

2. Step 2: Verify version and scope

   Version 4.11.0 is correct and scope should be 'test' to use Mockito only during testing.

3. Final Answer:

   Correct Maven dependency with version 4.11.0 and test scope -> Option A

4. Quick Check:

   Maven dependency with test scope = org.mockito mockito-core 4.11.0 test [OK]

Hint: Use 'mockito-core' with test scope and correct version [OK]

Common Mistakes:

• Omitting the test scope
• Using wrong artifactId like 'mockito-all'
• Using incorrect or too new version

3. You want to use Mockito in a JUnit 5 project with Gradle. Which of the following Gradle dependency setups correctly adds Mockito version 4.11.0 only for test implementation?

easy

A. testImplementation 'org.mockito:mockito-core:4.11.0'

B. implementation 'org.mockito:mockito-core:4.11.0'

C. compileOnly 'org.mockito:mockito-core:4.11.0'

D. runtimeOnly 'org.mockito:mockito-core:4.11.0'

Solution

1. Step 1: Understand Gradle scopes

   testImplementation means the dependency is available only during test compilation and runtime.

2. Step 2: Choose correct scope for Mockito

   Mockito is used only in tests, so testImplementation is the correct scope.

3. Final Answer:

   testImplementation 'org.mockito:mockito-core:4.11.0' -> Option A

4. Quick Check:

   Mockito test dependency = testImplementation [OK]

Hint: Use testImplementation for test-only dependencies in Gradle [OK]

Common Mistakes:

• Using implementation instead of testImplementation
• Using compileOnly which excludes runtime
• Using runtimeOnly which excludes compile time

4. Given the following JUnit test code snippet using Mockito, what will be the output of System.out.println(mockService.getData());?

import static org.mockito.Mockito.*;

public class ServiceTest {
  @Test
  void testGetData() {
    DataService mockService = mock(DataService.class);
    when(mockService.getData()).thenReturn("Mocked Data");
    System.out.println(mockService.getData());
  }
}

medium

A. Original data from DataService

B. null

C. Throws NullPointerException

D. Mocked Data

Solution

1. Step 1: Understand mock behavior

   The mock object returns what is specified in when().thenReturn(), here "Mocked Data".

2. Step 2: Check the printed output

   Calling getData() on mockService returns "Mocked Data", so it prints that string.

3. Final Answer:

   Mocked Data -> Option D

4. Quick Check:

   Mockito when().thenReturn() sets output = Mocked Data [OK]

Hint: when().thenReturn() sets mock method output [OK]

Common Mistakes:

• Expecting null because it's a mock
• Assuming real method runs
• Thinking it throws an exception

5. Identify the error in the following Mockito setup code snippet:

import static org.mockito.Mockito.*;

public class UserServiceTest {
  @Mock
  UserRepository repo;

  @Test
  void testUser() {
    when(repo.findUser()).thenReturn(new User("Alice"));
    UserService service = new UserService(repo);
    assertEquals("Alice", service.getUserName());
  }
}

medium

A. Incorrect method name findUser() should be getUser()

B. UserService constructor should not accept repo

C. Missing MockitoAnnotations.openMocks(this) to initialize @Mock fields

D. assertEquals parameters are reversed

Solution

1. Step 1: Check @Mock initialization

   @Mock fields need initialization, usually by calling MockitoAnnotations.openMocks(this) in setup.

2. Step 2: Verify test setup completeness

   Without initialization, repo remains null causing NullPointerException when used.

3. Final Answer:

   Missing MockitoAnnotations.openMocks(this) to initialize @Mock fields -> Option C

4. Quick Check:

   @Mock requires initialization = Missing MockitoAnnotations.openMocks(this) to initialize @Mock fields [OK]

Hint: Always initialize @Mock with MockitoAnnotations.openMocks(this) [OK]

Common Mistakes:

• Forgetting to initialize @Mock fields
• Assuming @Mock works without setup
• Mixing method names without checking