title: What does User.destroy_all or User.delete_all do?
body: <p>I am working on a project that has the following cucumber step:</p>
  
  <pre><code>Given /^no registered users$/ do
    User.delete_all
  end
  </code></pre>
  
  <p>As a new RoR user this looks a little dangerous even though I'd be testing on our development database because our <code>User</code> table has actual data.  What is the line of code doing?</p>
  
  <p>Thanks!  </p>