One commit to restore the test, one to fix it, and the rest to reduce size.

Summary

Ref 669f720

• Restore the no-duplication logic in focusin/focusout testing
• Reduce size

   raw     gz Sizes
279073  82883 dist/jquery.js
 88068  30594 dist/jquery.min.js

   raw     gz Compared to master @ 669f720edc4f557dfef986db747c09ebfaa16ef5
   +89   +209 dist/jquery.js
  -113    -28 dist/jquery.min.js

Checklist

• All authors have signed the CLA at https://cla.js.foundation/jquery/jquery
• New tests have been added to show the fix or feature works
• Grunt build and unit tests pass locally with these changes
• If needed, a docs issue/PR was created at https://github.com/jquery/api.jquery.com