- Spring Boot Testing
- Expert guide for testing Spring Boot 4 applications with modern patterns and best practices.
- Core Principles
- Test Pyramid
-
- Unit (fast) > Slice (focused) > Integration (complete)
- Right Tool
-
- Use the narrowest slice that gives you confidence
- AssertJ Style
-
- Fluent, readable assertions over verbose matchers
- Modern APIs
-
- Prefer MockMvcTester and RestTestClient over legacy alternatives
- Which Test Slice?
- Scenario
- Annotation
- Reference
- Controller + HTTP semantics
- @WebMvcTest
- references/webmvctest.md
- Repository + JPA queries
- @DataJpaTest
- references/datajpatest.md
- REST client + external APIs
- @RestClientTest
- references/restclienttest.md
- JSON (de)serialization
- @JsonTest
- See references/test-slices-overview.md
- Full application
- @SpringBootTest
- See references/test-slices-overview.md
- Test Slices Reference
- references/test-slices-overview.md
- - Decision matrix and comparison
- references/webmvctest.md
- - Web layer with MockMvc
- references/datajpatest.md
- - Data layer with Testcontainers
- references/restclienttest.md
- - REST client testing
- Testing Tools Reference
- references/mockmvc-tester.md
- - AssertJ-style MockMvc (recommended)
- references/mockmvc-classic.md
- - Traditional MockMvc
- references/resttestclient.md
- - Spring Boot 4+ REST client
- references/mockitobean.md
- - Mocking dependencies
- Assertion Libraries
- references/assertj-basics.md
- - Core AssertJ patterns
- references/assertj-collections.md
- - Collection assertions
- Testcontainers
- references/testcontainers-jdbc.md
- - PostgreSQL, MySQL, etc.
- Test Data Generation
- references/instancio.md
- - Generate complex test objects (3+ properties)
- Performance & Migration
- references/context-caching.md
- - Speed up test suites
- references/sb4-migration.md
- - Spring Boot 4.0 changes
- Quick Decision Tree
- Testing a controller endpoint?
- Yes → @WebMvcTest with MockMvcTester
- Testing repository queries?
- Yes → @DataJpaTest with Testcontainers (real DB)
- Testing business logic in service?
- Yes → Plain JUnit + Mockito (no Spring context)
- Testing external API client?
- Yes → @RestClientTest with MockRestServiceServer
- Testing JSON mapping?
- Yes → @JsonTest
- Need full integration test?
- Yes → @SpringBootTest with minimal context config
- Spring Boot 4 Highlights
- RestTestClient
-
- Modern alternative to TestRestTemplate
- @MockitoBean
-
- Replaces @MockBean (deprecated)
- MockMvcTester
-
- AssertJ-style assertions for web tests
- Modular starters
-
- Technology-specific test starters
- Context pausing
- Automatic pausing of cached contexts (Spring Framework 7)
Testing Best Practices
Code Complexity Assessment
When a method or class is too complex to test effectively:
Analyze complexity
- If you need more than 5-7 test cases to cover a single method, it's likely too complex
Recommend refactoring
- Suggest breaking the code into smaller, focused functions
User decision
- If the user agrees to refactor, help identify extraction points
Proceed if needed
- If the user decides to continue with the complex code, implement tests despite the difficulty
Example of refactoring recommendation:
// Before: Complex method hard to test
public
Order
processOrder
(
OrderRequest
request
)
{
// Validation, discount calculation, payment, inventory, notification...
// 50+ lines of mixed concerns
}
// After: Refactored into testable units
public
Order
processOrder
(
OrderRequest
request
)
{
validateOrder
(
request
)
;
var
order
=
createOrder
(
request
)
;
applyDiscount
(
order
)
;
processPayment
(
order
)
;
updateInventory
(
order
)
;
sendNotification
(
order
)
;
return
order
;
}
Avoid Code Redundancy
Create helper methods for commonly used objects and mock setup to enhance readability and maintainability.
Test Organization with @DisplayName
Use descriptive display names to clarify test intent:
@Test
@DisplayName
(
"Should calculate discount for VIP customer"
)
void
shouldCalculateDiscountForVip
(
)
{
}
@Test
@DisplayName
(
"Should reject order when customer has insufficient credit"
)
void
shouldRejectOrderForInsufficientCredit
(
)
{
}
Test Coverage Order
Always structure tests in this order:
Main scenario
- The happy path, most common use case
Other paths
- Alternative valid scenarios, edge cases
Exceptions/Errors
- Invalid inputs, error conditions, failure modes
Test Production Scenarios
Write tests with real production scenarios in mind. This makes tests more relatable and helps understand code behavior in actual production cases.
Test Coverage Goals
Aim for 80% code coverage as a practical balance between quality and effort. Higher coverage is beneficial but not the only goal.
Use Jacoco maven plugin for coverage reporting and tracking.
Coverage Rules:
80+% coverage minimum
Focus on meaningful assertions, not just execution
What to Prioritize:
Business-critical paths (payment processing, order validation)
Complex algorithms (pricing, discount calculations)
Error handling (exceptions, edge cases)
Integration points (external APIs, databases)
Dependencies (Spring Boot 4)
<
dependency
< groupId
org.springframework.boot </ groupId
< artifactId
spring-boot-starter-test </ artifactId
< scope
test </ scope
</ dependency
< dependency
< groupId
org.springframework.boot </ groupId
< artifactId
spring-boot-starter-webmvc-test </ artifactId
< scope
test </ scope
</ dependency
< dependency
< groupId
org.springframework.boot </ groupId
< artifactId
spring-boot-testcontainers </ artifactId
< scope
test </ scope
</ dependency