title: What we add under dev_dependencies in flutter
body: <p>I have a silly question regarding dev_dependencies in flutter, I am planning to use <code>mock_cloud_firestore</code> and in its installation page it says that we need to add it in the <code>dependencies</code> section of pubspec.yaml</p>
  
  <p>I think <code>mock_cloud_firestore</code> is not a production dependency but a dev dependency if so why we need to add it under dependencies?</p>
  
  <p>Also what we add under <code>dev_dependencies</code>?</p>
  
  <p>Thanks.</p>