I am trying to run following test case and expecting only Web Layer @WebMvcTest will be tested and rest of the things will be mocked automatically.

Error

Caused by: java.lang.IllegalArgumentException: JPA metamodel must not be empty
    at org.springframework.util.Assert.notEmpty(Assert.java:479)
    at org.springframework.data.jpa.mapping.JpaMetamodelMappingContext.<init>(JpaMetamodelMappingContext.java:58)
    at org.springframework.data.jpa.repository.config.JpaMetamodelMappingContextFactoryBean.createInstance(JpaMetamodelMappingContextFactoryBean.java:68)
    at org.springframework.data.jpa.repository.config.JpaMetamodelMappingContextFactoryBean.createInstance(JpaMetamodelMappingContextFactoryBean.java:44)
    at org.springframework.beans.factory.config.AbstractFactoryBean.afterPropertiesSet(AbstractFactoryBean.java:142)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1808)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1758)
    ... 105 more

Test Code

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest;
import org.springframework.test.web.servlet.MockMvc;

import static org.hamcrest.Matchers.is;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
import static org.springframework.test.web.servlet.result.MockMvcResultHandlers.print;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.jsonPath;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;

@WebMvcTest(WelcomeController.class) // Loads only the web layer
public class TestWelcomeController {
    @Autowired
    private MockMvc mockMvc; // Provides MockMvc for performing requests
    
    @Test
    public void testGetBooking() throws Exception {
        mockMvc.perform(get("/"))
                .andDo(print())
                .andExpect(status().isOk())
                .andExpect(jsonPath("status", is("OK")))
        ;
    }
}

Please note WelcomeController does not depend on any other class and I was hoping it will work perfectly fine without loading anything else.

To fix this I have to replace

@WebMvcTest(WelcomeController.class)

with

@AutoConfigureMockMvc
@SpringBootTest

Everything works like a charm. What is happening if I have to mock everything in order to run this it means @WebMvcTesthas zero value in case if any entity is being used

Questions:

1. Does @WebMvcTest have any usage? if JPAs etc are used but directly not involved in Controller under test
2. @SprnigBootTest creates application context but mock Web Layer as the default webEnvironemnt = MOCK, and hence we use MockMvc which almost does everything simulating HTTP calls by Mocking and does not make any Network calls .
3. @SpringBootTest(webEnvironment = RANDOM_PORT)loads embedded web-server, Beladung and most other tutorials blogs still use MockMvc with this configuration, does MockMvc change its behaviour if webEnvironment is used? or it will still work the same?
4. What is the difference between web layer mocking in case of @WebMvcTestand @SpringBootTest(webEnvironment = RANDOM_PORT) I know SpringBootTest loads the application context as well, but is there any change on web layer mocking?