Phpml\Math\Set::cardinality PHP Method

    public function cardinality() : int
    {
        return count($this->elements);
    }

 public function testAdd()
 {
     $set = new Set(['B', 'A', 2, 1]);
     $set->addAll(['foo', 'bar']);
     $this->assertEquals(6, $set->cardinality());
 }