add tests for wp_list_filter

wpListeFilter.php claimed to test wp_list_filter but had no tests for it so I have added them

Trac ticket: https://core.trac.wordpress.org/ticket/53987

[pbearne]

removed duplicate code in https://core.trac.wordpress.org/ticket/53988

[SergeyBiryukov]

Thanks for the PR!

Just noting there also some existing tests for wp_list_filter() in tests/functions/wpListUtil.php.

It looks like:

• wpListFilter.php has tests for wp_filter_object_list() and wp_list_pluck().
• wpListUtil.php has tests for wp_list_pluck(), wp_list_filter(), wp_list_sort(), and the WP_List_Util class.

This could probably use some reorganization for clarity and to make sure the tests are not duplicated.

[SergeyBiryukov]

In 51663:

Tests: Move wp_list_pluck() tests to their own file.

The tests were partially duplicated in two separate files.

Follow-up to [431/tests], [28900], [38928], [42527].

See #53363, #53987.

[SergeyBiryukov]

In 51664:

Tests: Remove duplicate wp_list_pluck() tests.

The tests were partially duplicated in two separate files, and are now located in their own file.

Follow-up to [431/tests], [28900], [38928], [42527], [51663].

See #53363, #53987.

[SergeyBiryukov]

In 51665:

Tests: Rename the test file and class for wp_filter_object_list() tests.

This matches the name of the function being tested.

Follow-up to [410/tests], [51663], [51664].

See #53363, #53987.

[SergeyBiryukov]

In 51666:

Tests: Move wp_list_filter() tests to their own file.

This matches the name of the function being tested.

Follow-up to [38928], [51663-51665].

See #53363, #53987.

[SergeyBiryukov]

In 51667:

Tests: Move wp_list_sort() tests to their own file.

This matches the name of the function being tested.

Follow-up to [38928], [51663-51666].

See #53363, #53987.

[SergeyBiryukov]

In 51668:

Coding Standards: Add missing visibility keywords for wp_filter_object_list() and wp_list_pluck() tests.

Follow-up to [51663-51667].

Props pbearne.
See #53363, #53987.

[SergeyBiryukov]

What's left here:

• See if wp_list_pluck() tests can be simplified further. Some use older fixtures and some use a data provider, so we could review the older fixtures and move them to the data provider too if it does not cover those cases yet.
• See if any additional tests for wp_list_filter() are necessary and not already covered by the data provider.