wordpress-develop/tests/phpunit/tests/link/getPreviewPostLink.php

<?php
/**
 * @group link
 * @covers ::get_preview_post_link
 */
class Tests_Link_GetPreviewPostLink extends WP_UnitTestCase {

	public function test_get_preview_post_link() {
		$post = self::factory()->post->create();

		$this->assertEquals( add_query_arg( 'preview', 'true', get_permalink( $post ) ), get_preview_post_link( $post ) );
	}

	public function test_get_preview_post_link_should_add_additional_query_vars() {
		$post = self::factory()->post->create();

		$expected = add_query_arg(
			array(
				'foo'     => 'bar',
				'bar'     => 'baz',
				'preview' => 'true',
			), get_permalink( $post )
		);

		$this->assertEquals(
			$expected, get_preview_post_link(
				$post, array(
					'foo' => 'bar',
					'bar' => 'baz',
				)
			)
		);
	}

	public function test_get_preview_post_link_should_use_custom_base_preview_link() {
		$post = self::factory()->post->create();

		$expected = 'https://google.com/?foo=bar&bar=baz&preview=true';

		$this->assertEquals(
			$expected, get_preview_post_link(
				$post, array(
					'foo' => 'bar',
					'bar' => 'baz',
				), 'https://google.com/'
			)
		);
	}

	public function test_get_preview_post_link_should_return_null_for_non_existent_post() {
		$this->assertNull( get_preview_post_link() );
		$this->assertNull( get_preview_post_link( 9999 ) );
		$this->assertNull( get_preview_post_link( 'foo' ) );
	}

	public function test_get_preview_post_link_for_global_post() {
		$post = self::factory()->post->create_and_get();

		$GLOBALS['post'] = $post;

		$this->assertEquals( add_query_arg( 'preview', 'true', get_permalink( $post ) ), get_preview_post_link() );
	}

	public function test_get_preview_post_link_should_return_empty_string_for_non_viewable_post_type() {
		$post_type = register_post_type(
			'non_viewable_cpt', array(
				'public' => false,
			)
		);

		$post = self::factory()->post->create(
			array(
				'post_type' => $post_type->name,
			)
		);

		$this->assertSame( '', get_preview_post_link( $post ) );
	}

}