Add unit tests for the llms-txt configuration

[leonidasmi]

Context

Summary

This PR can be summarized in the following changelog entry:

• Adds unit tests for the llms-txt configuration.

Relevant technical choices:

Test instructions

Test instructions for the acceptance test before the PR gets merged

This PR can be acceptance tested by following these steps:

• N/A

Relevant test scenarios

• Changes should be tested with the browser console open
• Changes should be tested on different posts/pages/taxonomies/custom post types/custom taxonomies
• Changes should be tested on different editors (Default Block/Gutenberg/Classic/Elementor/other)
• Changes should be tested on different browsers
• Changes should be tested on multisite

QA can test this PR by following these steps:

• N/A

Impact check

This PR affects the following parts of the plugin, which may require extra testing:

• None

UI changes

• This PR changes the UI in the plugin. I have added the 'UI change' label to this PR.

Other environments

• This PR also affects Shopify. I have added a changelog entry starting with [shopify-seo], added test instructions for Shopify and attached the Shopify label to this PR.

Documentation

• I have written documentation for this change. For example, comments in the Relevant technical choices, comments in the code, documentation on Confluence / shared Google Drive / Yoast developer portal, or other.

Quality assurance

• I have tested this code to the best of my abilities.
• During testing, I had activated all plugins that Yoast SEO provides integrations for.
• I have added unit tests to verify the code works as intended.
• If any part of the code is behind a feature flag, my test instructions also cover cases where the feature flag is switched off.
• I have written this PR in accordance with my team's definition of done.
• I have checked that the base branch is correctly set.

Innovation

• No innovation project is applicable for this PR.
• This PR falls under an innovation project. I have attached the innovation label.
• I have added my hours to the WBSO document.

Fixes #

[coveralls]

Pull Request Test Coverage Report for Build 5879e5a50f47b9dc7f0ae637458a78fa97f9b0f8

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 48 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-0.9%) to 52.779%

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Files with Coverage Reduction	New Missed Lines	%
admin/tracking/class-tracking-settings-data.php	7	0.0%
inc/options/class-wpseo-option-wpseo.php	18	86.49%
src/helpers/current-page-helper.php	23	74.31%

Totals
Change from base Build a2bd7e124e8fda2c486937b59f8a306770f2e0af:	-0.9%
Covered Lines:	30181
Relevant Lines:	58203

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💛 - Coveralls

[vraja-pro]

CR ✅
If we mock the variable, lets mention it in the type

[vraja-pro]

CR & AC ✅