Mockito Mocking Patterns

Name: mocking
Rating: 76
Author: comeredon

Setup

xml

<dependency>
    <groupId>org.mockito</groupId>
    <artifactId>mockito-junit-jupiter</artifactId>
    <version>5.8.0</version>
    <scope>test</scope>
</dependency>

java

@ExtendWith(MockitoExtension.class)
class ServiceTest {
    @Mock private CustomerRepository mockRepo;
    @InjectMocks private CustomerProcessor processor;
}

Stubbing

java

when(mockRepo.findById("12345")).thenReturn(testCustomer);
when(mockRepo.findById("00000")).thenThrow(new RecordNotFoundException());

Verifying Interactions

java

verify(mockRepo).findById("12345");
verify(mockRepo, never()).deleteById(anyString());
verify(mockRepo, times(2)).findById(anyString());

Argument Captors

java

@Captor ArgumentCaptor<String> captor;

verify(mockWriter).println(captor.capture());
assertEquals("expected output", captor.getValue());

When to Mock vs Use Real Objects

Mock	Real Object
Database/file I/O	Value objects (CustomerRecord)
External APIs	Pure functions
Email services	Simple calculations
Slow operations	Utility classes

Rules

•Never mock the class under test
•Don't over-mock — only mock external dependencies
•Use @ExtendWith(MockitoExtension.class) for cleaner code
•For void methods, use doThrow().when(mock).method()