Add post and search parameter tests for WP Query args.

[BE-Webdesign]

Add WP_Query arg tests for 's', 'p', 'name', 'page_id', 'page_slug', 'post_parent', 'post_parent__in', 'post_parent__not_in', 'post__in', 'post__not_in', 'post_name__in', 'post_type', 'post_status'