title: Cloud Functions for Firebase: functions.pubsub.topic('testTopic').onPublish not called
body: <p>I've copied this code snippet from the official documentation of cloud functions:</p>
  
  <pre><code>exports.helloPubSub = functions.pubsub.topic('testTopic').onPublish(event =&gt; {
      return console.log("test topic event data", event.data) 
  })
  </code></pre>
  
  <p>The topic exists, the function is deployed successfully; if I send a message to it, the message arrives to the devices, BUT this function does not get called. </p>
  
  <p>Anyone some help?</p>