Custom rspec formatter that prints the duration of each example

timestamp_formatter.rb

require 'rspec/core/formatters/progress_formatter'

class TimestampFormatter < RSpec::Core::Formatters::ProgressFormatter
  def example_started(example)
    @last_start = Time.new
    super(example)
  end

  def example_passed(example)
    time_diff = Time.now - @last_start
    output.print green(". #{'%8.5f' % time_diff} #{example.full_description}\n")
  end

  def example_failed(example)
    time_diff = Time.now - @last_start
    output.print "F #{'%8.5f' % time_diff} #{example.full_description}\n"
  end
end