Navigation Block: Add test coverage to check that post content is not removed

[ockham]

What?

Add a unit test to cover #59991 (fixed in #60071). The issue was that if a navigation menu was renamed (but not changed otherwise), its content was accidentally deleted.

The reason for this was related to the stdClass object that's used to communicate required changes to wp_update_post: If its post_content field was not set (indicating no changes were to be made), block_core_navigation_update_ignore_hooked_blocks_meta would accidentally set that field to an empty string (meaning it would be replaced by that) -- thus causing loss of data.

Why?

To prevent against regressions.

How?

Verify that if the stdClass object's post_content is unset before running block_core_navigation_update_ignore_hooked_blocks_meta, it also is afterwards.

Testing Instructions

Verify that tests pass.

To verify that the test covers the issue, revert 7b6ac8d (i.e. #60071), rebuild Gutenberg, and re-run the tests. They should now fail.

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Co-authored-by: ockham <bernhard-reiter@git.wordpress.org>
Co-authored-by: Mamaduka <mamaduka@git.wordpress.org>

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[Mamaduka]

Thank you, @ockham!

[ellatrix]

Can/should this test be backported to core?

[getdave]

My understanding is that this test provides coverage for the Navigation block. The block is maintained in the Gutenberg repo and therefore tests reside in the Gutenberg repo. At least that's what I picked up from Riad as the state of things during the Editor Tech lead role for WP 6.5.