应用程序测试返回"NullInjectorError:没有位置提供程序！“

import { NgModule } from '@angular/core';
import { MyService } from './my.service';

@NgModule({
  declarations: [
    // 组件声明
  ],
  imports: [
    // 模块导入
  ],
  providers: [MyService], // 声明服务提供者
  bootstrap: [AppComponent]
})
export class AppModule { }

import { Component } from '@angular/core';
import { MyService } from './my.service';

@Component({
  selector: 'app-my-component',
  templateUrl: './my-component.component.html',
  styleUrls: ['./my-component.component.css'],
  providers: [MyService] // 在组件级别声明服务提供者
})
export class MyComponent {
  constructor(private myService: MyService) {}
}

import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';
import { MyModule } from './my.module';

@NgModule({
  declarations: [
    // 组件声明
  ],
  imports: [
    CommonModule,
    MyModule // 导入包含服务提供者的模块
  ],
  exports: [
    MyModule
  ]
})
export class AnotherModule { }

import { Injectable } from '@angular/core';

@Injectable({
  providedIn: 'root' // 在根模块中自动提供
})
export class MyService {
  getData() {
    return 'Hello, World!';
  }
}

import { Component } from '@angular/core';
import { MyService } from './my.service';

@Component({
  selector: 'app-my-component',
  templateUrl: './my-component.component.html',
  styleUrls: ['./my-component.component.css']
})
export class MyComponent {
  constructor(private myService: MyService) {}

  ngOnInit() {
    console.log(this.myService.getData());
  }
}