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

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