my_formatter.rb

require 'rspec/core/formatters/progress_formatter'
require 'awesome_print'

class MyFormatter < RSpec::Core::Formatters::ProgressFormatter
  def start_dump
    super
    current_hash = examples_to_hash(examples)
    if File.exist? 'result.txt'
      lines = read_log 'result.txt'
      previous_hash = lines_to_hash lines
      all_tests = (previous_hash.keys + current_hash.keys).uniq
      affected_tests = all_tests.select do |description|
        current_result = current_hash[description]
        previous_result = previous_hash[description]
        current_result != previous_result
      end
      if affected_tests.empty?
        output.puts "No changes since last run"
      else
        output.puts "Affected tests (#{affected_tests.size}). "
        output.puts "PS CS Description"
        affected_tests.each do |description|
          current_result = current_hash[description]
          previous_result = previous_hash[description]
          output.puts([previous_result, current_result, description] * '  ')
        end
        output.puts "PS - Previous Status"
        output.puts "CS - Current Status"
      end
    end
    write_log('result.txt', current_hash)
    #    ap examples.first.execution_result
  end

  def write_log(file_name, hash)
    File.open(file_name, 'w') do |f|
      f.puts(hash.map{|descr,status| "#{status} #{descr}"})
    end
  end

  def read_log(file_name)
    lines = []
    File.open(file_name, 'r') do |f|
      s = nil
      lines << s while s = f.gets
    end
    lines
  end

  def examples_to_hash(examples)
    h = Hash.new('?')
    examples.each do |example|
      status = example.execution_result[:status]
      h[example.full_description] = result_to_char(status)
    end
    h
  end

  def result_to_char(result)
    case result
    when 'passed' then '.'
    when 'failed' then 'F'
    when 'pending' then 'P'
    else '?'
    end
  end

  def lines_to_hash(lines)
    h = Hash.new('?')
    lines.each do |line|
      next if line.size <= 3
      result = line[0..0]
      description = line[2..-1].chomp
      h[description] = result
    end
    h
  end
end