From ef24c69c624f080ae04f7d29345d50a340f31c61 Mon Sep 17 00:00:00 2001
From: Andrey Lushnikov <lushnikov@chromium.org>
Date: Thu, 9 May 2019 17:15:33 -0700
Subject: [PATCH] fix(tracing): start without options (#4388)

---
 docs/api.md          | 4 ++--
 lib/Tracing.js       | 6 +++---
 test/tracing.spec.js | 6 ++++++
 3 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/docs/api.md b/docs/api.md
index b01dd5e7064..845fadc850c 100644
--- a/docs/api.md
+++ b/docs/api.md
@@ -180,7 +180,7 @@
 - [class: Touchscreen](#class-touchscreen)
   * [touchscreen.tap(x, y)](#touchscreentapx-y)
 - [class: Tracing](#class-tracing)
-  * [tracing.start(options)](#tracingstartoptions)
+  * [tracing.start([options])](#tracingstartoptions)
   * [tracing.stop()](#tracingstop)
 - [class: Dialog](#class-dialog)
   * [dialog.accept([promptText])](#dialogacceptprompttext)
@@ -2319,7 +2319,7 @@ await page.goto('https://www.google.com');
 await page.tracing.stop();
 ```
 
-#### tracing.start(options)
+#### tracing.start([options])
 - `options` <[Object]>
   - `path` <[string]> A path to write the trace file to.
   - `screenshots` <[boolean]> captures screenshots in the trace.
diff --git a/lib/Tracing.js b/lib/Tracing.js
index 37fc8410b6e..b76674fcd3e 100644
--- a/lib/Tracing.js
+++ b/lib/Tracing.js
@@ -31,9 +31,9 @@ class Tracing {
   }
 
   /**
-   * @param {!{path: string, screenshots?: boolean, categories?: !Array<string>}} options
+   * @param {!{path?: string, screenshots?: boolean, categories?: !Array<string>}} options
    */
-  async start(options) {
+  async start(options = {}) {
     assert(!this._recording, 'Cannot start recording trace while already recording trace.');
 
     const defaultCategories = [
@@ -75,7 +75,7 @@ class Tracing {
 
   /**
    * @param {string} handle
-   * @param {string} path
+   * @param {?string} path
    */
   async _readStream(handle, path) {
     let eof = false;
diff --git a/test/tracing.spec.js b/test/tracing.spec.js
index f89e3b8d5ce..ffa054388d3 100644
--- a/test/tracing.spec.js
+++ b/test/tracing.spec.js
@@ -66,6 +66,12 @@ module.exports.addTests = function({testRunner, expect, defaultBrowserOptions, p
       const buf = fs.readFileSync(outputFile);
       expect(trace.toString()).toEqual(buf.toString());
     });
+    it('should work without options', async({page, server, outputFile}) => {
+      await page.tracing.start();
+      await page.goto(server.PREFIX + '/grid.html');
+      const trace = await page.tracing.stop();
+      expect(trace).toBeTruthy();
+    });
     it('should return null in case of Buffer error', async({page, server}) => {
       await page.tracing.start({screenshots: true});
       await page.goto(server.PREFIX + '/grid.html');