Tests: Add tests for get_boundary_post() working on non-singular pages

src/wp-includes/link-template.php

@@ -2209,9 +2209,13 @@ function prev_post_rel_link( $title = '%title', $in_same_term = false, $excluded
  * @return array|null Array containing the boundary post object if successful, null otherwise.
  */
 function get_boundary_post( $in_same_term = false, $excluded_terms = '', $start = true, $taxonomy = 'category' ) {
+	if ( ! taxonomy_exists( $taxonomy ) ) {
+		return null;
+	}
+
 	$post = get_post();
 
-	if ( ! $post || ! is_single() || is_attachment() || ! taxonomy_exists( $taxonomy ) ) {
+	if ( $in_same_term && ! $post ) {
 		return null;
 	}
 

tests/phpunit/tests/link/getBoundaryPost.php

@@ -0,0 +1,153 @@
+<?php
+
+/**
+ * @group link
+ * @covers ::get_boundary_post
+ */
+class Tests_Link_GetBoundaryPost extends WP_UnitTestCase {
+
+	/**
+	 * An array of post IDs.
+	 *
+	 * @var int[]
+	 */
+	protected static $post_ids;
+
+	/**
+	 * Set up the test fixture.
+	 *
+	 * @param WP_UnitTest_Factory $factory
+	 */
+	public static function wpSetUpBeforeClass( WP_UnitTest_Factory $factory ) {
+		// Create posts with specific dates to establish clear boundaries.
+		self::$post_ids = array(
+			'first'  => $factory->post->create( array( 'post_date' => '2020-01-01 12:00:00' ) ),
+			'middle' => $factory->post->create( array( 'post_date' => '2021-01-01 12:00:00' ) ),
+			'last'   => $factory->post->create( array( 'post_date' => '2022-01-01 12:00:00' ) ),
+		);
+	}
+
+	/**
+	 * @ticket 22957
+	 */
+	public function test_should_work_on_non_singular_pages() {
+		// Navigate to the homepage, which is not a single post page.
+		$this->go_to( home_url( '/' ) );
+		$this->assertFalse( is_single(), 'This test should be running on a non-single page.' );
+
+		// Test for the first post ($start = true, $in_same_term = false).
+		$first_boundary_post = get_boundary_post( false, '', true );
+		$this->assertIsArray( $first_boundary_post, 'get_boundary_post() should return an array for the first post.' );
+		$this->assertNotEmpty( $first_boundary_post, 'get_boundary_post() should not return an empty value for the first post.' );
+		$this->assertSame( self::$post_ids['first'], $first_boundary_post[0]->ID, 'The first boundary post ID is incorrect.' );
+
+		// Test for the last post ($start = false, $in_same_term = false).
+		$last_boundary_post = get_boundary_post( false, '', false );
+		$this->assertIsArray( $last_boundary_post, 'get_boundary_post() should return an array for the last post.' );
+		$this->assertNotEmpty( $last_boundary_post, 'get_boundary_post() should not return an empty value for the last post.' );
+		$this->assertSame( self::$post_ids['last'], $last_boundary_post[0]->ID, 'The last boundary post ID is incorrect.' );
+	}
+
+	/**
+	 * @ticket 22957
+	 */
+	public function test_should_return_null_for_in_same_term_without_current_post() {
+		// Navigate to a search results page with no matches, so there is no current post.
+		$this->go_to( home_url( '/?s=no-matching-posts' ) );
+		$this->assertNull( get_post(), 'This test should be running without a current post.' );
+
+		$this->assertNull( get_boundary_post( true ) );
+	}
+
+	/**
+	 * @ticket 22957
+	 */
+	public function test_should_still_work_on_single_pages() {
+		// Navigate to a single post page.
+		$this->go_to( get_permalink( self::$post_ids['middle'] ) );
+		$this->assertTrue( is_single(), 'This test should be running on a single page.' );
+
+		// Test for the first post ($start = true).
+		$first_boundary_post = get_boundary_post( false, '', true );
+		$this->assertIsArray( $first_boundary_post, 'get_boundary_post() should return an array on a single page.' );
+		$this->assertNotEmpty( $first_boundary_post, 'get_boundary_post() should not return an empty value for the first post on a single page.' );
+		$this->assertSame( self::$post_ids['first'], $first_boundary_post[0]->ID, 'The first boundary post ID is incorrect on a single page.' );
+
+		// Test for the last post ($start = false).
+		$last_boundary_post = get_boundary_post( false, '', false );
+		$this->assertIsArray( $last_boundary_post, 'get_boundary_post() should return an array for the last post on a single page.' );
+		$this->assertNotEmpty( $last_boundary_post, 'get_boundary_post() should not return an empty value for the last post on a single page.' );
+		$this->assertSame( self::$post_ids['last'], $last_boundary_post[0]->ID, 'The last boundary post ID is incorrect on a single page.' );
+	}
+
+	/**
+	 * @ticket 22957
+	 */
+	public function test_should_work_on_archive_pages() {
+		// Create a category and assign posts to test archive functionality.
+		$cat_id = self::factory()->category->create();
+		wp_set_post_categories( self::$post_ids['first'], array( $cat_id ) );
+		wp_set_post_categories( self::$post_ids['last'], array( $cat_id ) );
+
+		// Navigate to a category archive page.
+		$this->go_to( get_category_link( $cat_id ) );
+		$this->assertTrue( is_category(), 'This test should be running on a category archive page.' );
+
+		// Test boundary posts work on archive pages.
+		$first_boundary_post = get_boundary_post( false, '', true );
+		$this->assertIsArray( $first_boundary_post );
+		$this->assertNotEmpty( $first_boundary_post );
+		$this->assertSame( self::$post_ids['first'], $first_boundary_post[0]->ID );
+
+		$last_boundary_post = get_boundary_post( false, '', false );
+		$this->assertIsArray( $last_boundary_post );
+		$this->assertNotEmpty( $last_boundary_post );
+		$this->assertSame( self::$post_ids['last'], $last_boundary_post[0]->ID );
+	}
+
+	/**
+	 * @ticket 22957
+	 */
+	public function test_should_respect_in_same_term_parameter() {
+		// Create categories.
+		$cat1 = self::factory()->category->create();
+		$cat2 = self::factory()->category->create();
+
+		// Assign different categories to posts.
+		wp_set_post_categories( self::$post_ids['first'], array( $cat1 ) );
+		wp_set_post_categories( self::$post_ids['middle'], array( $cat1 ) );
+		wp_set_post_categories( self::$post_ids['last'], array( $cat2 ) );
+
+		// Navigate to the middle post to provide current post context.
+		$this->go_to( get_permalink( self::$post_ids['middle'] ) );
+		$this->assertTrue( is_single(), 'This test should be running on a single page.' );
+
+		// Test with $in_same_term = true (should find posts in same category as current post).
+		$first_boundary_post = get_boundary_post( true, '', true );
+		$this->assertIsArray( $first_boundary_post );
+		$this->assertSame( self::$post_ids['first'], $first_boundary_post[0]->ID, 'Should find first post in same category.' );
+
+		$last_boundary_post = get_boundary_post( true, '', false );
+		$this->assertIsArray( $last_boundary_post );
+		$this->assertSame( self::$post_ids['middle'], $last_boundary_post[0]->ID, 'Should find middle post as last in same category.' );
+
+		// Test with $in_same_term = false (should work normally across all posts).
+		$first_boundary_post_all = get_boundary_post( false, '', true );
+		$this->assertIsArray( $first_boundary_post_all );
+		$this->assertSame( self::$post_ids['first'], $first_boundary_post_all[0]->ID );
+
+		$last_boundary_post_all = get_boundary_post( false, '', false );
+		$this->assertIsArray( $last_boundary_post_all );
+		$this->assertSame( self::$post_ids['last'], $last_boundary_post_all[0]->ID );
+	}
+
+	/**
+	 * @ticket 22957
+	 */
+	public function test_should_return_null_for_invalid_taxonomy() {
+		$this->go_to( home_url( '/' ) );
+
+		$boundary_post = get_boundary_post( false, '', true, 'nonexistent_taxonomy' );
+		$this->assertNull( $boundary_post, 'get_boundary_post() should return null for non-existent taxonomy.' );
+	}
+}