Operation callback testing API

gistfile1.txt

triggerOperationCallback([delay])
  Trigger an operation callback.

  If 'delay' is given, it must be a positive integer; wait that many operation
  callback opportunities to trigger the callback. (Note that delay counts only
  work when we are running a body function from 'withOperationCallback'.)

withOperationCallback(body, [callback])
  Call the function 'body', establishing the function 'callback' as the
  operation callback while 'body' runs. Once 'body' completes, restore the
  runtime's original operation callback. Return whatever value or throw whatever
  exception 'body' did.

  If 'callback' returns normally, resume execution in 'body'. If 'callback'
  returns a positive integer, trigger another operation callback after that many
  operation callback opportunities have passed. (Thus, if 'callback' returns
  zero, trigger another operation callback at the next opportunity.)

  If 'callback' throws or is terminated, then that is propagated to 'body'.

  While 'callback' runs, we temporarily restore the original operation callback.
  When we resume execution in 'body', 'callback' is reinstated.

  If 'callback' is omitted, then let triggering an operation callback simply
  terminate the execution of 'body' (as if by the 'terminate' function).