wordpress-develop/tests/phpunit/tests/functions/isNewDay.php

<?php
/**
 * Test is_new_date() function.
 *
 * @since 5.2.0
 *
 * @group functions.php
 */
class Tests_Functions_IsNewDate extends WP_UnitTestCase {

	/**
	 * @ticket 46627
	 * @dataProvider _data_is_new_date
	 *
	 * @param string $currentday_string  The day of the current post in the loop.
	 * @param string $previousday_string The day of the previous post in the loop.
	 * @param bool   $expected           Expected result.
	 */
	public function test_is_new_date( $currentday_string, $previousday_string, $expected ) {
		global $currentday, $previousday;

		$currentday  = $currentday_string;
		$previousday = $previousday_string;

		$this->assertSame( $expected, is_new_day() );
	}

	public function _data_is_new_date() {
		return array(
			array( '21.05.19', '21.05.19', 0 ),
			array( '21.05.19', '20.05.19', 1 ),
			array( '21.05.19', false, 1 ),
		);
	}

}