Spring Boot How to init a Bean for testing?

In Spring Boot, we can create a @TestConfiguration class to initialize some beans for testing class only.

P.S Tested with Spring Boot 2

1. @TestConfiguration + @Import

This @TestConfiguration class will not pick up by the component scanning, we need to import it manually.

package com.mkyong;
import org.springframework.boot.test.context.TestConfiguration;
import org.springframework.boot.web.client.RestTemplateBuilder;
import org.springframework.context.annotation.Bean;
import java.time.Duration;
@TestConfiguration
public class TestConfig {
    @Bean
    public RestTemplateBuilder restTemplateBuilder() {
        return new RestTemplateBuilder()
                .basicAuthentication("mkyong", "password")
                .setConnectTimeout(Duration.ofSeconds(5));

package com.mkyong;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.web.client.TestRestTemplate;
import org.springframework.context.annotation.Import;
import org.springframework.test.context.junit4.SpringRunner;
@RunWith(SpringRunner.class)
@SpringBootTest
@Import(TestConfig.class)
public class RestTemplateTest {
    @Autowired
    private TestRestTemplate restTemplate;
    @Test
    public void post_user_ok() {
        //...

2. @TestConfiguration + Inner Static Class

Alternatively, create a inner class like this :

package com.mkyong;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.context.TestConfiguration;
import org.springframework.boot.test.web.client.TestRestTemplate;
import org.springframework.boot.web.client.RestTemplateBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.test.context.junit4.SpringRunner;
import java.time.Duration;
@RunWith(SpringRunner.class)
@SpringBootTest
public class RestTemplateTest {
    @TestConfiguration
    static class TestConfig {
        @Bean
        public RestTemplateBuilder restTemplateBuilder() {
            return new RestTemplateBuilder()
                    .basicAuthentication("mkyong", "password")
                    .setConnectTimeout(Duration.ofSeconds(5));
    @Autowired
    private TestRestTemplate restTemplate;
    @Test
    public void post_user_ok() {
        //...