spec/im/Primitive/Container/ContainerSpec.php
protected function plusLengthCheck($add = 1)
    {
        $this->all()->shouldHaveCount(count($this->initializer) + $add);
        $this->length->shouldBe(count($this->initializer) + $add);
    }
protected function plusLengthCheck($add = 1)
    {
        $this->all()->shouldHaveCount(count($this->initializer) + $add);
        $this->length->shouldBe(count($this->initializer) + $add);
    }
Checks length equal to $this->initializer plus $add

@param $add