diff --git a/lib/Tracing.js b/lib/Tracing.js
index 9d55e752..f82b319d 100644
--- a/lib/Tracing.js
+++ b/lib/Tracing.js
@@ -27,6 +27,7 @@ class Tracing {
 
   /**
    * @param {Object=} options
+   * @return {!Promise}
    */
   async start(options = {}) {
     console.assert(!this._recording, 'Cannot start recording trace while already recording trace.');
@@ -50,6 +51,7 @@ class Tracing {
 
   /**
    * @param {string} path
+   * @return {!Promise}
    */
   async stop(path) {
     let fulfill;
@@ -64,7 +66,7 @@ class Tracing {
 
   /**
    * @param {string} handle
-   * @param {string=} path
+   * @param {string} path
    * @return {!Promise}
    */
   async _readStream(handle, path) {
diff --git a/test/test.js b/test/test.js
index f1dc8fbb..b8e9f0b2 100644
--- a/test/test.js
+++ b/test/test.js
@@ -1361,7 +1361,7 @@ describe('Page', function() {
   });
 
   describe('Page.pdf', function() {
-    let outputFile = __dirname + '/assets/output.pdf';
+    const outputFile = __dirname + '/assets/output.pdf';
     afterEach(function() {
       fs.unlinkSync(outputFile);
     });