Build/Test Tools: Add test coverage for the get_posts_navigation() function.

This changeset adds a test case to verify that `get_the_posts_navigation()` only includes the "Older posts" and "Newer" posts links when appropriate.

Props jongycastillo, michelmany, joyously, geisthanen, SergeyBiryukov, mukesh27, audrasjb, costdev, sun, chrisbaltazar.
Fixes #55751.


git-svn-id: https://develop.svn.wordpress.org/trunk@55429 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/link/getThePostsNavigation.php

@@ -0,0 +1,108 @@
+<?php
+
+/**
+ * Tests get_the_posts_navigation function.
+ *
+ * @since 6.2.0
+ *
+ * @group link
+ *
+ * @covers ::get_the_posts_navigation
+ */
+class Tests_Link_GetThePostsNavigation extends WP_UnitTestCase {
+
+	/**
+	 * Creates posts before any tests run.
+	 *
+	 * @param WP_UnitTest_Factory $factory
+	 */
+	public static function wpSetUpBeforeClass( WP_UnitTest_Factory $factory ) {
+		$factory->post->create_many( 3 );
+	}
+
+	/**
+	 * Tests that get_the_posts_navigation() only includes the "Older posts" and "Newer" posts
+	 * links when appropriate.
+	 *
+	 * @ticket 55751
+	 *
+	 * @dataProvider data_get_the_posts_navigation
+	 *
+	 * @param int  $per_page  Posts per page to be queried.
+	 * @param int  $paged_num Pagination page number.
+	 * @param bool $older     Whether an "Older posts" link should be included.
+	 * @param bool $newer     Whether a "Newer posts" link should be included.
+	 */
+	public function test_get_the_posts_navigation( $per_page, $paged_num, $older, $newer ) {
+		global $wp_query, $paged;
+
+		$paged    = $paged_num;
+		$wp_query = new WP_Query(
+			array(
+				'post_type'      => 'post',
+				'posts_per_page' => $per_page,
+				'paged'          => $paged,
+			)
+		);
+
+		$actual = get_the_posts_navigation();
+
+		if ( $older ) {
+			$this->assertStringContainsString(
+				'Older posts',
+				$actual,
+				'Posts navigation must contain an "Older posts" link.'
+			);
+		}
+
+		if ( $newer ) {
+			$this->assertStringContainsString(
+				'Newer posts',
+				$actual,
+				'Posts navigation must contain a "Newer posts" link.'
+			);
+		}
+
+		if ( ! $older && ! $newer ) {
+			$this->assertEmpty(
+				$actual,
+				'Posts navigation must be an empty string.'
+			);
+		}
+	}
+
+	/**
+	 * Data provider.
+	 *
+	 * @return array[]
+	 */
+	public function data_get_the_posts_navigation() {
+		return array(
+			'older posts'                 => array(
+				'post_per_page' => 1,
+				'paged_num'     => 1,
+				'older'         => true,
+				'newer'         => false,
+			),
+			'newer posts'                 => array(
+				'post_per_page' => 1,
+				'paged_num'     => 3,
+				'older'         => false,
+				'newer'         => true,
+			),
+			'newer posts and older posts' => array(
+				'post_per_page' => 1,
+				'paged_num'     => 2,
+				'older'         => true,
+				'newer'         => true,
+			),
+			'empty posts'                 => array(
+				'post_per_page' => 3,
+				'paged_num'     => 1,
+				'older'         => false,
+				'newer'         => false,
+			),
+		);
+	}
+
+}