I'm not finding an easy way to test that in render_duotone_support() function with an empty $block_content, we are not returning early like we did before.

I tried checking that get_all_global_style_block_names() is called, but, as is a private static function, I couldn't make it work with getMockBuilder or ReflectionMethod

Any help would be kindly appreciated.

EDIT: Tests done 😄

Hi there!

Pinging @tellthemachines for a review 😅
Thanks a lot!!

== Patch Report

Patch tested: https://patch-diff.githubusercontent.com/raw/WordPress/wordpress-develop/pull/5540.diff

How to read this report:
🐞 <= Bug occurs.
✅ <= Behavior is ''expected''.
❌ <= Behavior is ''NOT expected''.

==== Environment

• OS: macOS 14.0
• Web Server: Nginx

• macOS 14.0
• PHP 8.2.11
• 6.4-RC1-56475-src
• Firefox 118.0.2

==== Steps to Reproduce

1. With WordPress 6.4 installed
2. Create the three posts with featured image, and another three without featured image.
3. On the site editor, in home page, TT4, add pagination to the Query Loop, set it to inherit the template settings, activate "Enhanced Pagination feature)
4. Add duotone to the feature image inside the Query Loop.
5. Make sure the three posts shown in the home page don't have featured image. Use pagination.
6. 🐞 Check that on page two, duotone filter is not applied for next posts.

==== Steps to Test Patch

1. 🛠 Apply [https://patch-diff.githubusercontent.com/raw/Backport/55415 make duotone support compatible with enhanced pagination #5540.diff the patch].
2. Refresh the home page.
3. ✅ Check that the duotone filter is applied after navigating to the second page.
4. ✅ Check that the navigation happened without a page reload.

==== Test Results

• ✅ Issue is reproducible.
• ✅ Issue resolved with patch.

==== Screenshots
Before patch:

After patch:

For commit prep, I'll be pushing a few commits to this PR to address the failing PHP 8.3 test, review notes from @aaronjorbin, resetting the reflected property's visibility in the test, and a few other minor formatting things.

Committed via https://core.trac.wordpress.org/changeset/56991.