set_trace_func

As an update to a previous article,

if $specs_timed.nil? && ENV.has_key?('SLOW')
  $specs_timed = true
  $timings = []

  Spec::Example::ExampleGroup.prepend_before do
    @start = Time.now
  end
  Spec::Example::ExampleGroup.append_after do
    elapsed = Time.now - @start
    if elapsed > ENV['SLOW'].to_f
      $timings << [elapsed, "#{self.class.description} #{description}"]
    end
  end

  at_exit do
    puts "\nSlow Specs:"
    $timings.sort{|a,b| a.first <=> b.first}.each do |time, name|
      puts " %7.4f #{name}" % time
    end
    puts "  None!" if $timings.empty?
  end
end

Then, simply run

rake SLOW=0.1

Two gotchas if you're using Rails though: instead of hooking S::E::ExampleGroup, you'll need to hook Spec::Rails::Example::RailsExampleGroup. Second, if you have any spec failures the timings don't seem to get output, since spec/rails aborts execution after failing.