Angular 2 单元测试：如何覆盖 TestBed 中的单个提供程序（用于服务的单元测试，而不是具有服务依赖项的组件）？

Question

I have:

beforeEach(() => {
   TestBed.configureTestingModule({
        providers: [
            DocumentsLoaderSvc,
           { provide: MgrSvc, useClass: MockMgrSvc },
           { provide: URLLoaderSvc, useClass:  MockURLLoaderSvcWhenData}
        ]
    });
});

How do I override URLLoaderSvc with another mock, in an "it" case with its own unique requirement? Is there something like TestBed.overrideProvider... Right now, I have each it statement in its own "describe", with its own beforeEach.

Answer 1

Maybe your best bet is to just make the mock configurable to suit the needs of different test cases. Keep it as an instance and use useValue instead of useClass

let urlLoderSvc: URLLoaderSvc;

beforeEach(() => {
  urlLoaderSvc = new URLLoaderSvc();

  TestBed.configureTestingModule({
     providers: [
        DocumentsLoaderSvc,
        { provide: MgrSvc, useClass: MockMgrSvc },
        { provide: URLLoaderSvc, useValue: urlLoaderSvc }
     ]
  });
});

Now in your it test cases, you can just configure the urlLoaderSvc instance to do whatever you want.

Answer 2

You can use ts-mockery and Mock.extend in every beforeEach where you need it. The problem here is that the service at this point is already injected in the component - re-providing it will not update the already injected instance. You would need to create your fixture for every test where you change the provided instances in this case. It is easier to have a flexible mock instance instead which you can configure before every test.

But sometimes it is needed, yes, for example if you have something like a repository service which needs an http service call and this call would need to be tested for success, fail and blocking to make sure that the repo service reacts correctly.