JUnit Testing Skills Guide

Quick reference to 15 JUnit testing skills for Spring Boot applications. See individual skill files for complete details.

Skills Overview

Testing by Layer

Controllers

unit-test-controller-layer

File: skills/unit-test-controller-layer/SKILL.md

MockMvc testing: request/response handling, status codes.

When to use:

• Testing REST endpoints
• Verifying request mappings
• Testing path variables and query params

Pattern:

@WebMvcTest(UserController.class)
class UserControllerTest {
    @Autowired MockMvc mockMvc;
    
    @Test
    void shouldReturnUser() throws Exception {
        mockMvc.perform(get("/users/1"))
            .andExpect(status().isOk())
            .andExpect(jsonPath("$.id").value(1));
    }
}

Services

unit-test-service-layer

File: skills/unit-test-service-layer/SKILL.md

Service testing: mocking, assertions, test organization.

When to use:

• Testing business logic
• Mocking dependencies
• Verifying service contracts

unit-test-exception-handler

File: skills/unit-test-exception-handler/SKILL.md

Testing custom exceptions and error scenarios.

When to use:

• Testing error cases
• Custom exception handling
• Exception messages

Data Layer

unit-test-mapper-converter

File: skills/unit-test-mapper-converter/SKILL.md

Entity to DTO mapping and converter testing.

When to use:

• Testing entity mappers
• Custom converters
• Bi-directional mappings

Cross-Cutting Concerns

unit-test-security-authorization

File: skills/unit-test-security-authorization/SKILL.md

Spring Security testing: @WithMockUser, roles, permissions.

When to use:

• Testing secured endpoints
• Verifying user roles
• Authorization checks

Pattern:

@Test
@WithMockUser(roles = "ADMIN")
void adminCanDelete() throws Exception {
    mockMvc.perform(delete("/users/1"))
        .andExpect(status().isNoContent());
}

unit-test-caching

File: skills/unit-test-caching/SKILL.md

Testing @Cacheable and cache eviction.

When to use:

• Cache hit/miss scenarios
• Cache eviction
• Cache configuration

unit-test-application-events

File: skills/unit-test-application-events/SKILL.md

Testing @EventListener and event publishing.

When to use:

• Event publishing tests
• Listener verification
• Event ordering

unit-test-config-properties

File: skills/unit-test-config-properties/SKILL.md

Testing @ConfigurationProperties binding.

When to use:

• Property binding validation
• Configuration tests
• Environment-specific configs

Specialized Testing

Async & Scheduled

unit-test-scheduled-async

File: skills/unit-test-scheduled-async/SKILL.md

Testing @Async and @Scheduled tasks.

When to use:

• Async method execution
• Scheduled job testing
• TestScheduler usage

Data Serialization

unit-test-json-serialization

File: skills/unit-test-json-serialization/SKILL.md

JSON serialization/deserialization with @JsonTest.

When to use:

• Testing JSON conversion
• Custom serializers
• Field naming and annotations

Parameterized Tests

unit-test-parameterized

File: skills/unit-test-parameterized/SKILL.md

JUnit 5 @ParameterizedTest for multiple scenarios.

When to use:

• Testing multiple input cases
• Reducing test duplication
• Edge case coverage

Pattern:

@ParameterizedTest
@ValueSource(ints = {1, 2, 3, 4, 5})
void shouldProcess(int value) {
    assertTrue(service.isValid(value));
}

Utilities & Boundary Conditions

unit-test-utility-methods

File: skills/unit-test-utility-methods/SKILL.md

Static methods, helpers, utility functions.

When to use:

• Testing utility classes
• Static factory methods
• Helper functions

unit-test-boundary-conditions

File: skills/unit-test-boundary-conditions/SKILL.md

Edge cases, limits, null values, boundary testing.

When to use:

• Boundary value analysis
• Null handling
• Limit testing

External Integration

unit-test-wiremock-rest-api

File: skills/unit-test-wiremock-rest-api/SKILL.md

REST API mocking with WireMock for integration tests.

When to use:

• Mocking external APIs
• Stubbing HTTP responses
• Testing integration points

Common Testing Workflows

Testing REST Endpoint

1. unit-test-controller-layer      → Test request/response
2. unit-test-service-layer         → Test business logic
3. unit-test-exception-handler      → Test error cases
4. unit-test-parameterized          → Multiple scenarios

Testing Secure Endpoint

1. unit-test-security-authorization → Mock user/roles
2. unit-test-controller-layer       → Test permission checks
3. unit-test-exception-handler      → Test authorization failures

Testing Configuration

1. unit-test-config-properties      → Property binding
2. unit-test-service-layer          → Service uses config
3. unit-test-caching                → Cache config

Testing Async Operations

1. unit-test-scheduled-async        → Async method execution
2. unit-test-application-events     → Event publishing
3. unit-test-parameterized          → Multiple timing scenarios

Stack & Tools

• JUnit: 5.x (Jupiter)
• Mocking: Mockito, MockMvc
• Assertions: AssertJ
• Spring Test: Spring Boot Test
• WireMock: 3.x
• Testcontainers: 1.x

Best Practices

• ✅ One assertion per test or related assertions
• ✅ Descriptive test method names
• ✅ Use @ParameterizedTest for multiple inputs
• ✅ Mock external dependencies
• ✅ Test edge cases and boundaries
• ✅ Keep tests isolated and independent
• ✅ Use builders for complex test data

Note: For complete patterns and examples, see individual skill files in skills/