"245$a": [
  { "op": "regsub", "from": "foo", "to": "bar", "flags": "g" }
]
[download]

This seems like a good starting point. See neilwatson's article How to ask better questions using Test::More and sample data for the way forward. Once you have a few working test cases defined, the only thing left is to define about a million more, including generous edge and corner cases and exception cases! No problem. :)