find the first occurrence of '<IPDR>'      # fast
  walk the string to the end                 # fastish
  skip back to the last occurrence of 'test' # fast
  walk forward to end of string again        # fastish
  repeat last two steps for each additional occurrence of 'test'
    # slow - quadratic in the number of occurrences of 'test'
  (no more 'test's to try) signal failure    # done