context-caching.md

Context Caching

Optimize Spring Boot test suite performance through context caching.

How Context Caching Works

Spring's TestContext Framework caches application contexts based on their configuration "key". Tests with identical configurations reuse the same context.

What Affects the Cache Key

• @ContextConfiguration
• @TestPropertySource
• @ActiveProfiles
• @WebAppConfiguration
• @MockitoBean definitions
• @TestConfiguration imports

Cache Key Examples

Same Key (Context Reused)

@WebMvcTest(OrderController.class)
class OrderControllerTest1 {
  @MockitoBean private OrderService orderService;
}

@WebMvcTest(OrderController.class)
class OrderControllerTest2 {
  @MockitoBean private OrderService orderService;
}
// Same context reused

Different Key (New Context)

@WebMvcTest(OrderController.class)
@ActiveProfiles("test")
class OrderControllerTest1 { }

@WebMvcTest(OrderController.class)
@ActiveProfiles("integration")
class OrderControllerTest2 { }
// Different contexts loaded

Viewing Cache Statistics

Spring Boot Actuator

management:
  endpoints:
    web:
      exposure:
        include: metrics

Access: GET /actuator/metrics/spring.test.context.cache

Debug Logging

logging.level.org.springframework.test.context.cache=DEBUG

Optimizing Cache Hit Rate

Group Tests by Configuration

 tests/
   unit/           # No context
   web/            # @WebMvcTest
   repository/     # @DataJpaTest  
   integration/    # @SpringBootTest

Minimize @TestPropertySource Variations

Bad (multiple contexts):

@TestPropertySource(properties = "app.feature-x=true")
class FeatureXTest { }

@TestPropertySource(properties = "app.feature-y=true")
class FeatureYTest { }

Better (grouped):

@TestPropertySource(properties = {"app.feature-x=true", "app.feature-y=true"})
class FeaturesTest { }

Use @DirtiesContext Sparingly

Only when context state truly changes:

@Test
@DirtiesContext // Forces context rebuild after test
void testThatModifiesBeanDefinitions() { }

Best Practices

1. Group by configuration - Keep tests with same config together
2. Limit property variations - Use profiles over individual properties
3. Avoid @DirtiesContext - Prefer test data cleanup
4. Use narrow slices - @WebMvcTest vs @SpringBootTest
5. Monitor cache hits - Enable debug logging occasionally