https://spring.io/guides/gs/testing-web/

@WebMvcTest : 테스트에서 Spring Boot는 전체 컨텍스트가 아닌 웹 레이어 만 인스턴스화.
              여러 컨트롤러가 있는 응용 프로그램에서는 하나의 컨트롤러만 인스턴스화하도록 요청할 수도 있습니다.

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.mockito.Mockito.when;
import static org.springframework.security.test.web.servlet.request.SecurityMockMvcRequestPostProcessors.csrf;
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.status;

import java.util.ArrayList;
import java.util.List;

import org.junit.jupiter.api.DisplayName;
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.boot.test.mock.mockito.MockBean;
import org.springframework.test.web.servlet.MockMvc;
import org.springframework.test.web.servlet.MvcResult;

import com.eun.tutorial.dto.Book;
import com.eun.tutorial.service.BookService;

@WebMvcTest(MyWebMvcController.class)
class MyWebMvcControllerJTest {

	@Autowired
	private MockMvc mockMvc;

	@MockBean
	private BookService service;

	@Test
	@DisplayName("viewBooks 호출시 view-books 페이지를 리턴하고 데이터는 모킹된 데이터가 맞는지 확인")
	public void getBooks() throws Exception {
		List<Book> bookList = new ArrayList<Book>();
		Book book1 = Book.builder()
				.isbn("isbn1")
				.name("name1")
				.author("author1")
				.build();
		Book book2 = Book.builder()
				.isbn("isbn2")
				.name("name2")
				.author("author2")
				.build();
		bookList.add(book1);
		bookList.add(book2);
		
		when(service.getBooks()).thenReturn(bookList);
		MvcResult mvcResult = this.mockMvc.perform(get("/book/viewBooks").with(csrf()))
		.andDo(print())
		.andExpect(status().isOk())
		.andReturn();
		
		assertEquals(bookList, (List<Book>) mvcResult.getModelAndView().getModelMap().get("books"));
		assertEquals("view-books", mvcResult.getModelAndView().getViewName());
	}

}

package com.eun.tutorial.controller;

import static org.assertj.core.api.Assertions.assertThat;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.springframework.security.test.web.servlet.request.SecurityMockMvcRequestPostProcessors.csrf;
import static org.springframework.test.web.servlet.result.MockMvcResultHandlers.print;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;

import java.nio.charset.StandardCharsets;

import org.junit.jupiter.api.DisplayName;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
import org.springframework.http.converter.StringHttpMessageConverter;
import org.springframework.test.web.servlet.MockMvc;
import org.springframework.test.web.servlet.MvcResult;
import org.springframework.test.web.servlet.request.MockMvcRequestBuilders;
import org.springframework.test.web.servlet.setup.MockMvcBuilders;

@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
@AutoConfigureMockMvc
class MainControllerJTest {
	
	@Autowired
	MainController mainController;
	
	@Autowired
	MockMvc mockMvc;
	
	@Test
	public void contextLoads() throws Exception {
		assertThat(mainController).isNotNull();
	}
	
	@Test
	@DisplayName("MyWebMvcConfigurer.java 파일에서 CharacterEncodingFilter 설정 후 HTTP Get 방식에서 Request Param 전달 시 한글 안 깨짐")
	public void hello() throws Exception {
		String name = "홍길동";
		
		MvcResult mvcResult = mockMvc.perform(MockMvcRequestBuilders.get("/reqParam")
								.param("name", name)
								)
								.andDo(print())
								.andExpect(status().isOk())	
								.andReturn();
		
		String responseBody = mvcResult.getResponse().getContentAsString();
		
		assertEquals("Hello, "+name, responseBody);
		
	}
	
	@Test
	@DisplayName("MyWebMvcConfigurer.java 파일에서 CharacterEncodingFilter 설정 후 HTTP Post 방식에서 Request Param 전달 시 한글 안 깨짐")
	public void hello2() throws Exception {
		String name = "홍길동";
		
		MvcResult mvcResult = mockMvc.perform(MockMvcRequestBuilders.post("/reqParam")
								.param("name", name)
								.contentType("text/plain;charset=UTF-8")
								.with(csrf())
								)
								.andDo(print())
								.andExpect(status().isOk())	
								.andReturn();
		
		String responseBody = mvcResult.getResponse().getContentAsString();
		
		assertEquals("Hello, "+name, responseBody);
		
	}
	
	@Test
	@DisplayName("MockMvc 생성시 MessageConverters를 추가해줘야 HTTP Get 방식에서 Request Param 전달 시 한글 안 깨짐")
	public void hello3() throws Exception {
		String name = "홍길동";
		
		MockMvc mockMvc = MockMvcBuilders.standaloneSetup(MainController.class)
//							.addInterceptors(null)
							.setMessageConverters(new StringHttpMessageConverter(StandardCharsets.UTF_8))
							.build();
		
		MvcResult mvcResult = mockMvc.perform(MockMvcRequestBuilders.get("/reqParam")
								.param("name", name)
								)
								.andDo(print())
								.andExpect(status().isOk())	
								.andReturn();
		
		String responseBody = mvcResult.getResponse().getContentAsString();
		
		assertEquals("Hello, "+name, responseBody);
		
	}
}