class Minitest::BacktraceFilter

def filter bt
  return ["No backtrace"] unless bt
  return bt.dup if $DEBUG
  new_bt = bt.take_while { |line| line !~ /lib\/minitest/ }
  new_bt = bt.select     { |line| line !~ /lib\/minitest/ } if new_bt.empty?
  new_bt = bt.dup                                           if new_bt.empty?
  new_bt
end