build.sh

#!/bin/sh

gcc -o idunno idunno.c

idunno.c

#include <stdio.h>

int main() {
  long long first, second;

  puts("enter two integers");
  scanf("%lld %lld", &first, &second);
  printf("%d\n", first + second);
  return 0;
}

idunno_spec.rb

def idunno(a, b)
  out = nil
  IO.popen './idunno', 'r+' do |io|
    io.puts a
    io.puts b
    read = io.gets
    read = io.gets
    out = read.to_i
  end
end

describe 'idunno' do
  describe 'addition' do
    it 'adds 2 and 2 to make 4' do
      expect(idunno(2, 2)).to eq 4
    end

    it 'adds 2 and 3 to make 5' do
      expect(idunno(2, 3)).to eq 5
    end

    100.times do
      n1 = rand 2**31
      n2 = rand 2**31
      sum = n1 + n2
      it "adds #{n1} and #{n2} to make #{sum}" do
        expect(idunno(n1, n2)).to eq sum
      end
    end
  end
end