public function testSetDate()
 {
     $time = '2000-01-02T03:14:25';
     $immutable = new DateTimeImmutable($time);
     $control = new DateTimeImmutable($time);
     $mutable = new DateTime($time);
     $new = $immutable->setDate(2005, 10, 20);
     $mutable->setDate(2005, 10, 20);
     $this->assertNotSame($immutable, $new);
     $this->assertSame($control->format(DateTime::RFC3339), $immutable->format(DateTime::RFC3339));
     $this->assertSame($mutable->format(DateTime::RFC3339), $new->format(DateTime::RFC3339));
 }