package com.example.spring_test;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class SpringJUnitTestStartup {

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

3. Chúng ta cần tạo ra lớp BaseIntegrationTest thế này:

package com.example.spring_test.test;

import org.junit.jupiter.api.extension.ExtendWith;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
import org.springframework.boot.test.mock.mockito.MockBean;
import org.springframework.context.ApplicationContextInitializer;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit.jupiter.SpringExtension;

import com.example.spring_test.SpringJUnitTestStartup;
import com.example.spring_test.service.GoodByeService;
import com.example.spring_test.test.BaseIntegrationTest.Initializer;
import com.example.spring_test.test.BaseIntegrationTest.SomeTestConfiguration;

@ExtendWith(SpringExtension.class)
@SpringBootTest(
    classes = SpringJUnitTestStartup.class,
    webEnvironment = WebEnvironment.DEFINED_PORT
)
@ContextConfiguration(
    initializers = Initializer.class,
    classes = SomeTestConfiguration.class
)
public class BaseIntegrationTest {

    @MockBean
    protected GoodByeService goodByeService;

    public static class Initializer
        implements ApplicationContextInitializer {

        @Override
        public void initialize(ConfigurableApplicationContext applicationContext) {
            // init something
        }
    }

    public static class SomeTestConfiguration {

        @Bean
        public Object someBean() {
            return "someBean";
        }
    }
}

4. Cuối cùng chúng ta sẽ tạo ra lớp GoodbyeControllerTest thế này:

package com.example.spring_test.test;

import static org.mockito.Mockito.times;
import static org.mockito.Mockito.verify;
import static org.mockito.Mockito.when;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.content;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;

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.test.web.servlet.MockMvc;

@AutoConfigureMockMvc
public class GoodbyeControllerTest extends BaseIntegrationTest {

    @Autowired
    private MockMvc mockMvc;

    @Test
    public void helloAndGoodByeTest() throws Exception {
        // given
        final String who = "World";
        final String goodBye = "I will never say good bye";
        when(goodByeService.goodBye(who)).thenReturn(goodBye);

        // when
        // then
        final String expected = "Hello World! and " + goodBye;
        mockMvc.perform(get("/hello-and-goodbye?who=World"))
               .andExpect(status().isOk())
               .andExpect(content().string(expected));

        verify(goodByeService, times(1)).goodBye(who);
    }
}

Done!!!