Simplified rspec formatter, good for VS code terminal integration

custom_formatter.rb

class String
  # colorization
  def colorize(color_code)
    "\e[#{color_code}m#{self}\e[0m"
  end

  def red
    colorize(31)
  end

  def green
    colorize(32)
  end

  def yellow
    colorize(33)
  end

  def blue
    colorize(34)
  end

  def pink
    colorize(35)
  end

  def light_blue
    colorize(36)
  end
end

class CustomFormatter
  # This registers the notifications this formatter supports, and tells
  # us that this was written against the RSpec 3.x formatter API.
  RSpec::Core::Formatters.register self, :example_group_started, :example_group_finished, :example_started, :example_failed, :example_passed

  def initialize(output)
    @output = output
    @group_level = 0
  end

  def example_group_started(notification)
    @output.puts if @group_level == 0
    @output.puts "#{current_indentation}#{notification.group.description.strip}".green

    @group_level += 1
  end

  def example_group_finished(_notification)
    @group_level -= 1 if @group_level > 0
  end

  def example_started(notification)
    @output << (current_indentation + notification.example.description).yellow
  end

  def example_failed(notification)
    @output.puts '     Failed!!!!'.red
    @output << notification.exception.to_s.red
    @output.puts
    # custome your own rule
    backtraces = notification.formatted_backtrace.grep_v(/spec\/support/).grep_v(/rvm\/gems/)
    @output << backtraces.join("\r\n").blue
  end

  def example_passed(_notification)
    @output.puts '     Passed!'.light_blue
  end

  def current_indentation
    '  ' * @group_level
  end
end