Lesson Outline

Creating a Mock Backend

We keep hitting on the point that a unit test should be isolated - nothing comes in, and nothing goes out. If the unit test requires some input from an external dependency then we supply it with fake data.

In order to keep with this principle, we have been substituting our injected dependencies with mocked versions, like this:

providers: [
  { provide: ModulesService, useValue: {/* etc */} },
  { provide: NavController, useValue: {/* etc */} },
];

In tests that we are about to create, we will be dealing with code that makes an HTTP request to a server. We don't want the code in that test to actually send a request to our real server, we just want to check that the individual unit is doing its job - not that the entire system is working (again, that's not the role of a unit test).

When we want to make HTTP requests, we inject the HttpClient service into our constructor. Given the approach we have been using for mocking services so far, you would be correct in assuming that you should do something like this:

      providers: [
        ...
        { provide: HttpClient, useValue: {/* etc */} },
        ...
      ]