Spring Boot中的完全验证测试，注入失败

// src/main/java/com/example/demo/DemoApplication.java
package com.example.demo;

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

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

// src/main/java/com/example/demo/service/MyService.java
package com.example.demo.service;

import org.springframework.stereotype.Service;

@Service
public class MyService {
    public String sayHello() {
        return "Hello, World!";
    }
}

// src/main/java/com/example/demo/controller/MyController.java
package com.example.demo.controller;

import com.example.demo.service.MyService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class MyController {
    private final MyService myService;

    @Autowired
    public MyController(MyService myService) {
        this.myService = myService;
    }

    @GetMapping("/hello")
    public String sayHello() {
        return myService.sayHello();
    }
}

// src/test/java/com/example/demo/DemoApplicationTests.java
package com.example.demo;

import com.example.demo.service.MyService;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

import static org.assertj.core.api.Assertions.assertThat;

@SpringBootTest
public class DemoApplicationTests {

    @Autowired
    private MyService myService;

    @Test
    public void contextLoads() {
        assertThat(myService).isNotNull();
    }

    @Test
    public void testSayHello() {
        String result = myService.sayHello();
        assertThat(result).isEqualTo("Hello, World!");
    }
}