Phpml\Math\Set::contains PHP Method

    public function contains($element) : bool
    {
        return $this->containsAll([$element]);
    }

 public function testContains()
 {
     $set = new Set(['B', 'A', 2, 1]);
     $this->assertTrue($set->contains('B'));
     $this->assertTrue($set->containsAll(['A', 'B']));
     $this->assertFalse($set->contains('C'));
     $this->assertFalse($set->containsAll(['A', 'B', 'C']));
 }