title: Mock the length of a string
body: <p>I am trying to test (with Jasmine) validation of a description field (which is a knockout observable) with max length of 1000 characters;
  What I usually do is <code>expect(model.description().length).toBe(1000);</code> 
  to prove that my string is of the desired length.
  Is there any way to mock it somehow without the need to actually write a string of 1000 chars long?</p>