WebMvcTest需要在SpringBootApplication类中定义的模拟bean

Question

我正在使用@WebMvcTest来测试控制器。我观察到需要在测试类的SpringBoot应用程序类中模拟自动装配的bean。根据我的理解，使用@WebMvcTest可以独立测试控制器。只是想知道为什么我需要模拟SpringBootApplication类中使用的EmployeeService。以下是相关的类-

@RunWith(SpringRunner.class)
@WebMvcTest(EmployeeController.class)
public class EmployeeControllerTest {

   @Autowired
   MockMvc mockMvc;

   @MockBean
   EmployeeService employeeService;

   @Test
   public void getEmployee() throws Exception {
    mockMvc.perform(get("/employee")
                   .contentType(MediaType.APPLICATION_JSON))
                   .andExpect(status().isOk());
     }
  }

SpringBootApplication类

@SpringBootApplication
public class DemoApplication {

   @Autowired
   EmployeeService employeeService;

   public static void main(String[] args) {
       SpringApplication.run(DemoApplication.class, args);
   }
 }

EmployeeController

@RestController
public class EmployeeController {

   @GetMapping(value = "/employee")
   public Employee getEmployee() {
      return Employee.builder().
            name("Harry")
            .id("1")
            .build();
   }
 }

雇员豆

import lombok.Builder;
import lombok.Data;

@Data
@Builder
public class Employee {    
    private String id;
    private String name;
}

我正在使用SpringBoot版本2.1.6