MathPHP\SetTheory\Set::length PHP Метод

    public function length() : int
    {
        return count($this->A);
    }

 /**
  * @dataProvider dataProviderForSingleSet
  */
 public function testLength(array $members)
 {
     $set = new Set($members);
     $this->assertEquals(count($members), $set->length());
 }