Add filter to limit the sitemap date range

[kasparsd]

Fixes #146.

• Introduce the msm_sitemap_index filter which allows removing daily sitemaps from the root sitemap index.

[kasparsd]

This is ready for code review.

[GaryJones]

How about a test to demonstrate and prove how this new filter works in practice?

[kasparsd]

@GaryJones Are you thinking of a unit test for the filter? I'm not sure exactly what to test there since it is only a pass-through for a variable and the result depends purely on the filter implementation. In a pure unit test way it would just check if apply_filters() was called during build_root_sitemap_xml().

We've already added an example to the readme to illustrate a sample usage.

Did you have any other ideas in mind?

[GaryJones]

In a pure unit test way it would just check if apply_filters() was called during build_root_sitemap_xml().

Right - we're not testing how apply_filters() works, only that build_root_sitemap_xml() has the behaviour / logic such that the value is filterable.

[lgedeon]

I don't see any tests for build_root_sitemap_xml, but it appears that to test this I would need to:

• Create two posts on different dates using create_dummy_post
• Call MSM_SiteMap_Test::build_sitemaps
• Assert that the return value of build_root_sitemap_xml contains two date nodes
• Add a filter to remove everything before a date that falls between the two dates from the first step.
• Assert that the return value now contains one date node

@GaryJones, does this sound right? Also should this be added to test-sitemap-functions.php, test-sitemap-filter.php or somewhere else?

[GaryJones]

This should be properly documented.

[lgedeon]

@GaryJones This is documented now. What is next on the path to merger?