Angular 组件测试错误：TypeError 无法读取未定义的属性“订阅”

Question

我有一个简单的单元测试，它是在 Angular 6 组件上使用 karma/jasmine 完成的。从我收集的复数课程和文档看来，我正在正确地模拟我的组件所需的服务，但是当调用该方法从模拟服务返回数据时，我收到错误消息说属性订阅未定义。

我的“it”函数是空的，因为一旦在 beforeEach 方法中构造了组件，测试就会失败。组件的构造函数调用了我尝试测试的方法。请在下面查看我的代码。

import { TestBed, async, ComponentFixture } from '@angular/core/testing';
import { MainComponent } from './main.component';
import { DataService } from '../services/data.service';
import { of } from 'rxjs';
import { NO_ERRORS_SCHEMA } from "@angular/core";

describe('Should construct MainComponent', () => {
	let mainComponent: MainComponent;
	let EMPLOYEES;
	let fixture: ComponentFixture<MainComponent>;
	let mockDataService;

	beforeEach(() => {
		EMPLOYEES = [
			{
				"PrismEmployeeID": 1,
				"FirstName": "install2",
				"LastName": "account",
				"Initials": "IA ",
				"NickName": "",
				"SSN": "",
				"DateOfBirth": "09/26/2014",
				"HireDate": "09/26/2014",
				"OfficePhone": "9043943239",
				"OfficeFax": "9042246400",
				"ClassificationID": 133,
				"ClassificationDescription": "Claims Support U.S. Insurance",
				"SupervisorID": 32,
				"DepartmentID": 2,
				"DepartmentDescription": "Information Technology",
				"SupervisorName": "Jerry Sutton",
				"CountryID": 1,
				"CountryName": "United States"
			}
		];

		mockDataService = jasmine.createSpyObj(['GetEmployees']);

		TestBed.configureTestingModule({
			declarations: [MainComponent],
			providers: [{ provide: DataService, useValue: mockDataService }],
			schemas: [NO_ERRORS_SCHEMA]
		});

		fixture = TestBed.createComponent(MainComponent);
		fixture.detectChanges();

		mockDataService = jasmine.createSpyObj(['GetEmployees']);
	});

	it('should get an array Employees',
		() => {});
});

主组件

import { Component, Input, Output, OnInit, EventEmitter } from '@angular/core';
import { DataService } from '../services/data.service';
import { TableComponent } from './table/table.component';

@Component({
	selector: 'main',
	templateUrl: './main.component.html',
	styleUrls: ['./main.component.css']
})
export class MainComponent {
	columns: string[] = ['PrismEmployeeID', 'LastName', 'FirstName', 'Initials', 'LastFour', 'BirthDate', 'HireDate', 'OfficePhone', 'OfficeFax', 'ClassificationDescription', 'SupervisorName', 'DepartmentDescription', 'CountryName'];
	loading: boolean = false;
	@Input() tableData: Employee[];

	constructor(private _dataService: DataService) {
		this.loadEmployees();
	}

	loadEmployees() {
		this.loading = true;
		this._dataService.GetEmployees().subscribe((data) => {
			this.loading = false;
			this.tableData = data.json() as Employee[];
		});
	}

	onLoading(loading: boolean) {
		this.loading = loading;
	}

	onReloadData(reloadData: boolean) {
		this.loadEmployees();
	}
}

interface Employee {
	PrismEmployeeID: number;
	FirstName: string;
	LastName: string;
	Initials: string;
	NickName: string;
	SSN: string;
	DateOfBirth: string;
	HireDate: string;
	OfficePhone: string;
	OfficeFax: string;
	ClassificationID: number;
	ClassificationDescription: string;
	SupervisorID: number;
	DepartmentID: number;
	DepartmentDescription: string;
	SupervisorName: string;
	CountryID: number;
	CountryName: string;

	_selected: boolean;
}

<br/>
<h2>Prism Employees</h2>
<div *ngIf="loading" class="d-flex justify-content-center bd-highlight mb-3">
	<div class="p-2 bd-highlight"></div>
	<div class="p-2 bd-highlight">
		<mat-spinner id="overlay"></mat-spinner>
	</div>
	<div class="p-2 bd-highlight"></div>
</div>

<div *ngIf='tableData'>
  <table-component #table (loading)="onLoading($event)" (reloadData)="onReloadData($event)" [data]="tableData" [displayedColumns]="columns"></table-component>
</div>

Answer 1

问题是您当前提供的服务存根没有为 GetEmployees 方法配置返回值。这意味着一旦组件调用了前一个函数并订阅了它的（未定义的）返回，它就会触发一个异常。

要解决这个问题，您需要伪造该方法的返回。基于this answer，您可以尝试如下：

import {of} from 'rxjs';
...
mockDataService = jasmine.createSpyObj(DataService.Name, {'GetEmployees': of(EMPLOYEES)});
...

更新：

不过，为了使其正常工作，您必须重构您的 DataService.GetEmployees 方法以具有以下签名：

GetEmployees(): Observable<Employee[]>;

DataService.GetEmployees 的当前实现是一个leaky abstraction，因为它从旧的Http API 返回原始Response 对象，迫使消费者（在本例中为组件）了解有关底层实现的详细信息（这个细节是使用data.json() as Employee[]）

Answer 2

spyOn(mockYourService, 'getSomeData').and.returnValue({ subscribe: () => {} })

你可以... 在 spy 中返回一个实际的 observable

spyOn(mockYourService, 'getSomeData').and.returnValue(Observable.of(someData)) 也许这将比循环订阅方法更受欢迎，因为如果对服务的调用正在更改组件中的某些内容，那么您可能需要测试一下