The tests do not cover the Set::map() method which seems to have been added in version 1.2.7 of php-ds/ext-ds.
The Set\map trait has however been created long time ago but the inclusion in the SetTest class has been forgotten.

This oversight has probably caused the lack of implementation of Set::map() in php-ds/polyfill project.

IDEs using polyfill via project dependencies (composer require php-ds/php-ds) therefore indicate an error when using the map method on a Set.