要在Angular中使用真实API进行HTTP测试，可以使用以下步骤：

1. 创建一个服务(service)来处理API调用。可以使用Angular的HttpClient模块来发送HTTP请求。在服务中，可以定义各种API调用的方法，并返回Observable对象。

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Observable } from 'rxjs';

@Injectable({
  providedIn: 'root'
})
export class ApiService {
  private apiUrl = 'http://api.example.com'; // 替换为实际的API URL

  constructor(private http: HttpClient) { }

  getUsers(): Observable {
    return this.http.get(`${this.apiUrl}/users`);
  }

  getUser(id: number): Observable {
    return this.http.get(`${this.apiUrl}/users/${id}`);
  }

  // 其他API调用方法
}

2. 在组件(component)中使用该服务，并订阅Observable对象来获取API的响应。

import { Component, OnInit } from '@angular/core';
import { ApiService } from './api.service';

@Component({
  selector: 'app-users',
  template: `
    

      
{{ user.name }}
    
  `
})
export class UsersComponent implements OnInit {
  users: any[];

  constructor(private apiService: ApiService) { }

  ngOnInit() {
    this.apiService.getUsers().subscribe((response) => {
      this.users = response;
    });
  }
}

3. 在单元测试中，可以使用Angular的HttpClientTestingModule来模拟HTTP请求，并提供虚拟的HTTP响应。

import { TestBed, async, ComponentFixture } from '@angular/core/testing';
import { HttpClientTestingModule, HttpTestingController } from '@angular/common/http/testing';
import { UsersComponent } from './users.component';
import { ApiService } from './api.service';

describe('UsersComponent', () => {
  let component: UsersComponent;
  let fixture: ComponentFixture;
  let apiService: ApiService;
  let httpMock: HttpTestingController;

  beforeEach(async(() => {
    TestBed.configureTestingModule({
      imports: [HttpClientTestingModule],
      declarations: [UsersComponent],
      providers: [ApiService]
    }).compileComponents();

    fixture = TestBed.createComponent(UsersComponent);
    component = fixture.componentInstance;
    apiService = TestBed.inject(ApiService);
    httpMock = TestBed.inject(HttpTestingController);
  }));

  afterEach(() => {
    httpMock.verify();
  });

  it('should fetch users', () => {
    const mockUsers = [
      { id: 1, name: 'John' },
      { id: 2, name: 'Jane' }
    ];

    component.ngOnInit();

    const req = httpMock.expectOne('http://api.example.com/users');
    expect(req.request.method).toBe('GET');
    req.flush(mockUsers);

    expect(component.users).toEqual(mockUsers);
  });
});

在上面的示例中，我们首先导入HttpClientTestingModule和HttpTestingController，然后在beforeEach函数中创建测试模块并初始化组件、服务和HttpTestingController。在测试用例中，我们使用httpMock.expectOne来捕获HTTP请求，并使用req.flush来提供虚拟的HTTP响应。

这样我们就可以使用真实的API进行HTTP测试了。记得将示例中的API URL替换为实际的API URL。