Spring Boot testing: Zero to Hero by Daniel Garnier-Moiroux

Use @SpringBootTest for full integration tests but be aware it creates heavyweight test contexts that are cached (32 by default)

Test slices like @WebMvcTest, @DataJpaTest etc. load only required parts of the application context, making tests faster and more focused

Leverage Spring Boot’s test auto-configuration for mock MVC, security, database access rather than configuring manually

AssertJ provides fluent assertions that are more readable than standard JUnit assertions or Hamcrest matchers

Use TestContainers for integration tests requiring real databases or other services - Spring Boot has native support for it

@MockBean and @SpyBean can inject Mockito mocks into the Spring context for isolating components

Avoid overusing test contexts with different configurations as it increases test execution time and memory usage

The WebTestClient provides a modern API for testing web endpoints compared to MockMvc

Use @DynamicPropertySource to inject dynamic properties like container ports into tests

Spring Security test support enables testing secured endpoints with mock users and authentication

For async tests, use utilities like Awaitility instead of Thread.sleep()

Keep test contexts minimal and focused on what you’re actually testing to maintain fast execution times