Add unit tests for bookmarks-provider.js

[duggiefresh]

This gets 100% code coverage for the BookmarksProvider

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 64.12%. Comparing base (16f5d95) to head (4be1a0d).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1584      +/-   ##
==========================================
+ Coverage   63.70%   64.12%   +0.41%     
==========================================
  Files          68       68              
  Lines        6216     6216              
  Branches     1378     1378              
==========================================
+ Hits         3960     3986      +26     
+ Misses       2217     2191      -26     
  Partials       39       39              

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