title: Mock 'document' with Jasmine
body: <p>I'm using <code>document.hidden</code> and I need to mock it as <code>true</code> or <code>false</code> in my unit tests.
  So I made this:</p>
  
  <pre><code>documentMock = jasmine.createSpyObj('document', ['hidden']);
  
  module(function ($provide) {
      $provide.value('document', documentMock);
  });
  </code></pre>
  
  <p>But <code>hidden</code> is always returning false.</p>