Injecting dependent services when unit testing AngularJS services

Question

I'm testing service A, but service A depends on service B (i.e. service B is injected into service A).

I've seen this question but my case is a bit different because in my opinion it makes more sense to mock service B instead of injecting an actual instance of service B. I'd mock it with a jasmine spy.

Here's a sample test:

describe("Sample Test Suite", function() {

  beforeEach(function() {

    module('moduleThatContainsServiceA');

    inject([
      'serviceA', function(service) {
        this.service = service;
      }
    ]);

  });

  it('can create an instance of the service', function() {
    expect(this.service).toBeDefined();
  });
});

The error I get is:

Error: Unknown provider: serviceBProvider

How could I do something like this?

Answer 1

Actually in AngularJS Dependency Injection uses the 'last wins' rule. So you can define your service in your test just after including your module and dependencies, and then when service A that you're testing will request service B using DI, AngularJS will give mocked version of service B.

This is often is done by defining new module like MyAppMocks, putting mocked services/values there and then just adding this module as dependency.

Kind of (schematically):

beforeEach(function() {
  angular.module('MyAppMocks',[]).service('B', ...));
  angular.module('Test',['MyApp','MyAppMocks']);
  ...