如何监视作为BehaviorSubject/Observable的服务属性？遇spyOnProperty报错

Hey there, let's break down why you're hitting that error and walk through two solid fixes—including the method-based approach you already thought of!

The Root Cause #

That error pops up because spyOnProperty with the 'get' access type expects your user property to be a getter property (defined with the get keyword), but right now your UserService's user is just a regular, plain property. Jasmine can't spy on a getter that doesn't exist, hence the message.

Solution 1: Turn user into a Getter Property #

If you want to stick with using spyOnProperty, all you need to do is refactor your UserService to make user a getter. Here's how that would look:

// UserService.ts
import { Injectable } from '@angular/core';
import { Observable, of } from 'rxjs';

@Injectable({ providedIn: 'root' })
export class UserService {
  // Private backing field to hold the user observable internally
  private _user$: Observable<User> = of(defaultUser);

  // Getter for the user observable
  get user(): Observable<User> {
    return this._user$;
  }

  // Optional: Add a method if you need to update the user later
  updateUser(newUser: User): void {
    this._user$ = of(newUser);
  }
}

With this change, your original test code will work exactly as you wrote it:

spyOnProperty(userService, 'user', 'get').and.returnValue(Observable.of(adminUser));

Solution 2: Use a Method (Your Proposed Idea) #

If you'd rather avoid getters entirely, your plan to switch to a getUser() method is a great alternative. Here's how to implement that:

First, update the UserService to replace the direct property with a method:

// UserService.ts
@Injectable({ providedIn: 'root' })
export class UserService {
  private user$: Observable<User> = of(defaultUser);

  getUser(): Observable<User> {
    return this.user$;
  }
}

Next, update your component code to call userService.getUser().subscribe(...) instead of accessing userService.user directly. For testing, you'll spy on the method instead of the property:

spyOn(userService, 'getUser').and.returnValue(Observable.of(adminUser));

Both approaches work perfectly—pick whichever fits your code style better!

内容的提问来源于stack exchange，提问作者Ka Mok