ruby

def check_stability
  result = []
  1000.times{ result << yield }

  raise Exception, 'function is unstable' if result.uniq!.size > 1
  p "Result: #{result}"
end

arr = [{:id=>1, :val=>30}, {:id=>2, :val=>30}, {:id=>1002, :val=>82}]
check_stability do
  arr.sort{|x,y| y[:val] <=> x[:val]}.map{|x| x[:id]}
end
# Result: [[1002, 2, 1]]

arr = [{:id=>1, :val=>30}, {:id=>2, :val=>30}]
check_stability do
  result = arr.sort{|x,y| y[:val] <=> x[:val]}.map{|x| x[:id]}
end
# Result: [[1, 2]]