Tests: Add unit test for empty comment tags in export

[himanshupathak95]

Trac ticket: https://core.trac.wordpress.org/ticket/61244

This PR adds unit tests for the patch present to verify the behavior of comment filtering during exports.

The new test ensures that when comments are filtered out using get_comment filter, no empty <wp:comment> tags appear in the export XML.

Run the tests:

npm run test:php -- --filter=Tests_Admin_ExportWp 

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[desrosj]

Instead of output buffering within this method, can we utilize the get_the_export() method in this class to instead fetch the entire export XML string? Then the same checks can be performed using xpath().

[himanshupathak95]

can we utilize the get_the_export() method

Yes, I completely missed that. Thanks for pointing out.

[westonruter]

This looks good to me, but just a couple suggestions for the tests.

[himanshupathak95]

I think the failing test is unrelated to the changes in the PR.

[westonruter]

See also: https://core.trac.wordpress.org/ticket/61244#comment:31