title: Why my tests succeed without a running mongodb instance?
body: <p>My app uses mongodb and I have bunch tests that save/query and update data. </p>
  
  <p>I run my tests without a mongodb instance and they all pass! why?</p>
  
  <p>Is this a known feature? what is it called?</p>
  
  <p>Can someone please point me to the bit of documentation that confirms this?</p>