mocking
Provides Mockito mocking patterns and best practices for isolating unit tests from external dependencies.
Install
mkdir -p .claude/skills/mocking && curl -L -o skill.zip "https://agentskills.codes/api/skills/download/10482" && unzip -o skill.zip -d .claude/skills/mocking && rm skill.zipInstalls to .claude/skills/mocking
Activation
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Mockito mocking patterns for isolating units under test. Use when testing classes with external dependencies like databases, files, or APIs.Key capabilities
- →Stubbing external dependencies
- →Verifying method interactions
- →Capturing method arguments
- →Isolating units under test
How it works
Uses Mockito to create mock objects for external dependencies, allowing developers to stub behaviors and verify interactions during unit tests.
Inputs & outputs
When to use mocking
- →Stubbing database repository methods
- →Verifying interactions with external API clients
- →Testing void methods with argument captors
- →Isolating service classes from file system dependencies
About this skill
Mockito Mocking Patterns
Setup
<dependency>
<groupId>org.mockito</groupId>
<artifactId>mockito-junit-jupiter</artifactId>
<version>5.8.0</version>
<scope>test</scope>
</dependency>
@ExtendWith(MockitoExtension.class)
class ServiceTest {
@Mock private CustomerRepository mockRepo;
@InjectMocks private CustomerProcessor processor;
}
Stubbing
when(mockRepo.findById("12345")).thenReturn(testCustomer);
when(mockRepo.findById("00000")).thenThrow(new RecordNotFoundException());
Verifying Interactions
verify(mockRepo).findById("12345");
verify(mockRepo, never()).deleteById(anyString());
verify(mockRepo, times(2)).findById(anyString());
Argument Captors
@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()
When not to use it
- →When testing pure functions
- →When testing value objects
- →When the class under test is the target
Prerequisites
Limitations
- →Over-mocking can lead to brittle tests
- →Cannot mock static methods or constructors easily
How it compares
Provides a structured approach to isolation that avoids real I/O or slow operations compared to manual test setups.
Compared to similar skills
mocking side by side with the closest alternatives in the catalog.
| Skill | Installs | Updated | Safety | Difficulty |
|---|---|---|---|---|
| mocking (this skill) | 0 | 5mo | No flags | Beginner |
| unit-testing | 3 | 3mo | No flags | Beginner |
| springboot-verification | 4 | 4mo | Review | Intermediate |
| code-checklist | 0 | 4mo | Review | Beginner |
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