MockMvcTester vs RestTestClient - Which One Should You Use in Spring Boot 4?

Learn to choose between MockMvcTester and RestTestClient for testing Spring Boot 4 controllers through practical demonstrations and expert guidance from the Spring team. Explore the key differences between these two testing approaches, discover when to use each one, and master practical implementation techniques including @WebMvcTest, @MakitoBean (the successor to @MockBean), and @AutoConfigureRestTestClient configuration. Practice writing tests with AssertJ-style fluent assertions while understanding the unique capabilities of each approach, from MockMvcTester's server-side inspection and multi-file upload testing to RestTestClient's unified API for mock and real environments and typed object deserialization. Examine real code examples with a Book Controller and Repository setup, compare testing methodologies side-by-side, and gain insights into when MockMvcTester excels at server-side inspection versus when RestTestClient's unified approach provides better flexibility for different testing environments.