User:CFeng (WMF)/EspressoTest with Screenshots Comparison

Preparation
 * 1) An Android device, API >= 19
 * 2) A File Manager app

Setup If you cannot find the folder or cannot find any files inside the folder, please make sure the Storage Permission has been enabled.
 * 1) After installing the app, go to the App Info => Permissions to enable the Storage permission Enable permission storage.png
 * 2) Run the   to generate references (screenshots)
 * 3) Use the File Manager app to find the generated references, which should be exported to
 * 4) Copy the references into the Wikipedia Android app assets folder:

Test
 * 1) Run the   again
 * 2) Check the console to see the results of screenshot comparison

Notes
 * 1) If we need to test other pages (e.g.: Article page, Reading Lists page), please make sure the Network status is stable and every step should be only processed after the current page is loaded completely
 * 2) The resolution of the references and screenshots should be the same, otherwise, the comparison will be meanless.
 * 3) Automatically grants the Storage permission should be considered as an improvement.

Links
 * 1) Reference ticket: https://phabricator.wikimedia.org/T176860
 * 2) Patch of sample codes: https://gerrit.wikimedia.org/r/#/c/394735/