DevTools: Automagically detect user compiled content shell in npm test

third_party/WebKit/Source/devtools/readme.md

 # Chrome DevTools frontend
 
 The client-side of the Chrome DevTools, including all JS & CSS to run the DevTools webapp.
 
 It is available on NPM as the [chrome-devtools-frontend](https://www.npmjs.com/package/chrome-devtools-frontend) package. It's not currently available via CJS or ES2015 modules, so consuming this package in other tools may require [some effort](https://github.com/paulirish/devtools-timeline-model/blob/master/index.js).
 
 #### Package versioning
 The version number of the npm package (e.g. `1.0.373466`) refers to the Chromium commit position of latest frontend git commit. It's incremented with every Chromium commit, however the package is updated roughly daily.
 
 ### Source code
@@ skipping 19 matching lines @@
 > npm run chrome -- https://news.ycombinator.com
 > ```
 > (e.g. this launches Hacker News on startup)
 
 ### Hacking
 * DevTools documentation: [devtools.chrome.com](https://devtools.chrome.com)
 * [Debugging protocol docs](https://developer.chrome.com/devtools/docs/debugger-protocol) and [Chrome Debugging Protocol Viewer](http://chromedevtools.github.io/debugger-protocol-viewer/)
 * [awesome-chrome-devtools](https://github.com/paulirish/awesome-chrome-devtools): recommended tools and resources
 * Contributing to DevTools: [bit.ly/devtools-contribution-guide](http://bit.ly/devtools-contribution-guide)
 
+### Testing
+
+Basic:
+* `npm test` - builds devtools and runs all inspector layout tests
+
+> Note: If you're using a full chromium checkout and compiled content shell in out/Release, then `npm test` uses that. Otherwise, with only a front-end checkout (i.e. cloning from GitHub), then `npm test` will fetch a previously compiled content shell from the cloud (and cache it for future test runs).
+
+Advanced:
+* `npm test -- --fetch-content-shell` - even if you're using a full chromium checkout and have a compiled content shell, this will fetch a pre-compiled content shell. This is useful if you haven't compiled your content shell recently.
+* `npm test -- -f --child-processes=16` - pass in additional flags to the test harness
+* `npm test -- inspector/sources inspector/console` - run specific tests
+* `npm test -- inspector/cookie-resource-match.html --debug-devtools` - debug a specific test (non-bundled & minified). You can use "-d" as a shorthand for "--debug-devtools".
+* `npm run test:build` - only builds devtools (in debug mode)
+* `npm run test:run` - only runs devtools tests
 
 #### Development
 * All devtools commits: [View the log], [RSS feed] or [@DevToolsCommits] on Twitter
 * [All open DevTools tickets] on crbug.com
 * File a new DevTools ticket: [new.crbug.com](https://bugs.chromium.org/p/chromium/issues/entry?labels=OS-All,Type-Bug,Pri-2&components=Platform%3EDevTools)
 * Code reviews mailing list: [devtools-reviews@chromium.org]
 
 ### Getting in touch
 * [@ChromeDevTools] on Twitter
 * Chrome DevTools mailing list: [groups.google.com/forum/google-chrome-developer-tools](https://groups.google.com/forum/#!forum/google-chrome-developer-tools)
 
   [devtools-reviews@chromium.org]: https://groups.google.com/a/chromium.org/forum/#!forum/devtools-reviews
   [RSS feed]: https://feeds.peter.sh/chrome-devtools/
   [View the log]: https://chromium.googlesource.com/chromium/src/third_party/WebKit/Source/devtools/+log/master
   [@ChromeDevTools]: http://twitter.com/ChromeDevTools
   [@DevToolsCommits]: http://twitter.com/DevToolsCommits
   [all open DevTools tickets]: https://bugs.chromium.org/p/chromium/issues/list?can=2&q=component%3APlatform%3EDevTools&sort=&groupby=&colspec=ID+Stars+Owner+Summary+Modified+Opened