mynumber_validator.rb

class MyNumberValidator
  def validate(num)
    # write your code here...
  end
end

mynumber_validator_spec.rb

require './mynumber_validator'

RSpec.describe MyNumberValidator do
  let(:validator) { MyNumberValidator.new }

  describe '#validate_mynumber' do
    subject { validator.validate(num) }

    context 'pass the number that has invalid length ' do
      let(:num) { 12345678901 }
      it { is_expected.to be false }
    end

    context 'pass the invalid number' do
      let(:num) { 123456789012 }
      it { is_expected.to be false }
    end

    context 'pass the valid number' do
      let(:num) { 123456789018 }
      it { is_expected.to be true }
    end

    context 'pass the invalid number that calculated digit is bigger' do
      let(:num) { 123456789001 }
      it { is_expected.to be false }
    end

    context 'pass the valid number that calculated digit is bigger' do
      let(:num) { 123456789000 }
      it { is_expected.to be true }
    end

    context 'pass the invalid number as string' do
      let(:num) { '123456789012' }
      it { is_expected.to be false }
    end

    context 'pass the valid number starts with 0' do
      let(:num) { '023456789013' }
      it { is_expected.to be true }
    end
  end
end

question.md

Check Digit of MyNumber

How to calculate the check digit of mynumber

\begin{align*} d &= 11 - \Biggl( \sum^{11}{n=1} P_n \times Q_n \Biggr) \bmod 11 \ & \text{ただし，$\Biggl( \sum^{11}{n=1} P_n \times Q_n \Biggr) \bmod 11 \leq 1$の場合は$d=0$} \ P_n &= \text{ 個人番号を構成する検査用数字以外の十一桁の番号の最下位の桁を1桁目としたときの$n$桁目の数字} \ Q_n &= \begin{cases} n + 1 && \text{if $1 \leq n \leq 6$} \ n - 5 && \text{if $7 \leq n \leq 11$} \end{cases} \end{align*}

from: 総務省令第八十五号 行政手続における特定の個人を識別するための番号の利用等に関する法律