在 Angular 2 中对 observable 进行单元测试 [英] Unit testing an observable in Angular 2

问题描述

在 Angular 2 中对返回 Observable 结果的服务进行单元测试的正确方法是什么?假设我们在 CarService 服务类中有一个 getCars 方法:

What is the correct way of unit testing a service returning an Observable result in Angular 2? Let's say we have a getCars method in a CarService service class:

...
export class CarService{
    ...
    getCars():Observable<any>{
        return this.http.get("http://someurl/cars").map( res => res.json() );
    }
    ...
}

如果我尝试按以下方式编写测试，我会收到警告:SPEC HAS NO EXPECTATIONS":

If I try to write the tests in the following way I get the warning: 'SPEC HAS NO EXPECTATIONS':

it('retrieves all the cars', inject( [CarService], ( carService ) => {
     carService.getCars().subscribe( result => {         
         expect(result.length).toBeGreaterThan(0);
     } );       
}) );

使用 injectAsync 并没有帮助，因为据我所知，它适用于 Promise 对象.

Using injectAsync does not help because it works with Promise objects as far as I could see.

推荐答案

最后我以一个工作示例结束.Observable 类有一个 toPromise 方法，可以将 Observable 转换为 Promise 对象.正确的做法应该是:

Finally I end with a working example. Observable class has a method toPromise that converts an Observable to a Promise object. The correct way should be:

it('retrieves all the cars', injectAsync( [CarService], ( carService ) => {
  return carService.getCars().toPromise().then( (result) => {         
     expect(result.length).toBeGreaterThan(0);
  } );       
}) );

但是，虽然上面的代码适用于任何 Observable 对象，但我仍然遇到从 Http 请求返回的 Observable 的问题，这可能是一个错误.这是一个演示上述案例的 plunker:http://plnkr.co/edit/ak2qZH685QzTN6RoK71H?p=预览

更新:
从 beta.14 版本开始，它似乎可以与提供的解决方案一起正常工作.

But while to above code works with any Observable object, I still have the problem with the Observables returned from Http requests which is probably a bug. Here is a plunker demonstrating the case above: http://plnkr.co/edit/ak2qZH685QzTN6RoK71H?p=preview

Update:
As of version beta.14 it seems to work properly with the provided solution.

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