format() публичный Метод

See formatting options as in PHP date()
public format ( integer | string | DateTime | DateInterval $date, string $format ) : string
$date integer | string | DateTime | DateInterval
$format string
Результат string
 /**
  * @test
  * @dataProvider formatExamples
  */
 public function formatWorks($dateOrString, $format, $expected)
 {
     $helper = new DateHelper();
     $result = $helper->format($dateOrString, $format);
     $this->assertSame($expected, $result);
 }