title: Firebase Functions database trigger not firing
body: <p>I'm trying out Firebase Functions for the first time (Typescript). I have coded two functions: </p>
  
  <pre><code>export const helloWorld = functions.https.onRequest((request, response) =&gt; {
    response.send("Hello from Firebase!");
    const testRef = admin.database().ref("test");
    return testRef.set(true);
   });
  export const testRef = functions.database.ref("test").onWrite((event) =&gt; {
      console.log("Event: " + JSON.stringify(event))
      const testRef = admin.database().ref("test");
      return testRef.set(true);
  });
  </code></pre>
  
  <p><code>helloWorld</code> works as expected when I navigate to the relevant URL. <code>testRef</code> on the other hand doesn't trigger when I insert or modify data at the "test" location in the root of the Firebase. What am I doing wrong?</p>