\startmodule[ifchanged]

\startluacode
  local collected = {}
  local tobesaved = {}

  local function initializer()
      -- this function is not called!
      -- print("<><><><><>",collected)
      collected = utilitydata.thirddata.ifchanged.collected
  end

  job.register('thirddata.ifchanged.collected', tobesaved, initializer)

  local function cachedmd5sum(filename)
      return collected[filename] or ""
  end

  function commands.doiffilechangedelse(filename)
    local md5sum = md5.HEX(io.loaddata(filename) or "")
    local cached = cachedmd5sum(filename)
    tobesaved[filename] = md5sum
    print(">>>>>>>>>>>>", md5sum)
    print("============", cached)
    commands.testcase(md5sum == cached)
  end

\stopluacode

\def\doiffilechangedelse#1%
    {\ctxcommand{doiffilechangedelse("#1")}}

\def\doiffilechanged#1%
    {\doiffilechangedelse{#1}\firstofoneargument\gobbleoneargument}

\def\doiffilenotchanged#1%
    {\doiffilechangedelse{#1}\gobbleoneargument\firstofoneargument}

\stopmodule

\starttext
\doiffilechanged{test.pdf}{\executesystemcommand{context test}}
\stoptext