Media: Add new functions to return the previous/next attachment links.

New functions:

* get_adjacent_image_link()
* get_next_image_link()
* get_previous_image_link()

Fixes #45708.

Props flixos90, DrewAPicture, mor10, antpb, hellofromTonya, whyisjake.




git-svn-id: https://develop.svn.wordpress.org/trunk@51122 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/media/previousImageLink.php

@@ -0,0 +1,56 @@
+<?php
+
+require_once __DIR__ . '/testcase-adjacent-image-link.php';
+
+/**
+ * @group  media
+ * @covers ::previous_image_link
+ */
+class Tests_Media_PreviousImageLink extends WP_Test_Adjacent_Image_Link_TestCase {
+	protected $default_args = array(
+		'size' => 'thumbnail',
+		'text' => false,
+	);
+
+	/**
+	 * @ticket 45708
+	 *
+	 * @dataProvider data_previous_image_link
+	 */
+	function test_previous_image_link( $current_attachment_index, $expected_attachment_index = 0, $expected, array $args = array() ) {
+		list( $expected, $args ) = $this->setup_test_scenario( $current_attachment_index, $expected_attachment_index, $expected, $args );
+
+		$this->expectOutputString( $expected );
+		$this->assertNull( previous_image_link( ...$args ) );
+	}
+
+	public function data_previous_image_link() {
+		return array(
+			// Happy paths.
+			'when has previous link'           => array(
+				'current_attachment_index'  => 3,
+				'expected_attachment_index' => 2,
+				'expected'                  => '<a href=\'http://example.org/?attachment_id=%%ID%%\'><img width="1" height="1" src="http://example.org/wp-content/uploads/image2.jpg" class="attachment-thumbnail size-thumbnail" alt="" loading="lazy" /></a>',
+			),
+			'with text when has previous link' => array(
+				'current_attachment_index'  => 3,
+				'expected_attachment_index' => 2,
+				'expected'                  => '<a href=\'http://example.org/?attachment_id=%%ID%%\'>Some text</a>',
+				'args'                      => array( 'text' => 'Some text' ),
+			),
+
+			// Unhappy paths.
+			'when no previous link'            => array(
+				'current_attachment_index'  => 1,
+				'expected_attachment_index' => 0,
+				'expected'                  => '',
+			),
+			'with text when no previous link'  => array(
+				'current_attachment_index'  => 1,
+				'expected_attachment_index' => 0,
+				'expected'                  => '',
+				'args'                      => array( 'text' => 'Some text' ),
+			),
+		);
+	}
+}