Why does injecting 'ng' in unit tests change promise handling behaviour?

Question

The following service uses $q.when to wrap a third-party promise:

// service.js
angular.module('test', [])
  .service('pouchdb', function($q, $window) {
    var db = new $window.PouchDB('test');
    this.info = function() {
      return $q.when(db.info.apply(db, arguments));
    };
  });

Corresponding unit test:

describe('Failing Q when tests', function() {
  beforeEach(module('test'));

  var $rootScope, pouchdb;
  beforeEach(inject(function(_$rootScope_, pouchdb) {
    $rootScope = _$rootScope_;
    pouchdb = pouchdb;
  }));

  it('should resolve a promise', function(done) {
    // FIXME: never resolves
    pouchdb.info()
      .then(function(info) {
        expect(info).toBeDefined();
      })
      .finally(done);
    $rootScope.$apply();
  });
});

pouchdb.info never resolves and Jasmine times out. However, if I manually inject ng , the spec works as expected:

describe('Working Q when tests', function() {
  var pouchdb;
  beforeEach(function() {
    var $injector = angular.injector(['ng', 'test']);
    var pouchDB = $injector.get('pouchdb');
    pouchdb = pouchDB('db');
  });

  it('should resolve a promise', function(done) {
    pouchdb.info()
      .then(function(info) {
        expect(info).toBeDefined();
      })
      .finally(done);
  });
});

Could anyone explain why;

1. The first spec doesn't resolve
2. The second spec does (injecting ng )
3. It doesn't need $rootScope.$apply
4. Whether it's a good pattern to use

Answer 1

Are you using angular-mocks? https://docs.angularjs.org/api/ngMock

The only reason why I think that you'd need to inject 'ng' manually is if there is no ng-app initializing your app, at least according to https://docs.angularjs.org/api/ng/function/angular.module

If you use angular-mocks it takes care of that for you https://github.com/angular/angular.js/blob/master/src/ngMock/angular-mocks.js#L1785

Can't think of any other reason as to why this problem would occur.