title: No route matches with valid object
body: <p>Having read this:
  <a href="https://stackoverflow.com/questions/4628103/rspec-no-route-matches-error">&quot;No route matches&quot; error?</a></p>
  
  <p>I'm trying to figure out if there is a gem or way to monkey patch actionpack to get around this constraint.</p>
  
  <p>Basically, I'm writing specs (they run fast), and I don't understand why actionpack throws this error when being applied to an object which isn't "saved".</p>
  
  <p>For two reasons:</p>
  
  <ol>
  <li>Why is it throwing a "No route matches" when it really should be throwing something more meaningful (e.g. object must be saved before a route can be constructed, or object ID is nil). The exception seems a little obscure.</li>
  <li>I shouldn't have to save the object at all if all I am trying to do is generate a url for that object, given the ID is populated using a factory or something similar.</li>
  </ol>
  
  <p>This constraint makes it a pain to write fast tests, unless I'm missing something...</p>