Incrementing os.clock() in Lua - unit-testing

Question

Summary: Can I cause time to (appear to) pass in my script without busywaiting? Using os.execute('sleep 1') doesn't cut it (and also wastes time).
Details
I have a library that does work after specific intervals. I currently schedule this by injecting a table into a time-sorted list. Roughly:
local delayedWork = {}
function handleLater( data, delaySeconds )
local delayedItem = { data=data, execTime=os.clock() + delaySeconds }
local i=1
for _,existing in ipairs(delayedWork) do
if existing.execTime > delayedItem.execTime then break else i=i+1 end
end
table.insert(delayedWork,i,delayedItem)
end
Later on I periodically check for work to do. Roughly:
function processDelayedWork()
local i,last = 1,#delayedWork
while i<=last do
local delayedItem = delayedWork[i]
if delayedItem.execTime <= os.clock() then
table.remove(delayedWork,i)
-- use delayedItem.data
last = last-1
else
i=i+1
end
end
end
(The fact that this uses CPU time instead of wall time is an issue for a different question. The fact that I repeatedly shift the array during processing instead of one compacting pass is an optimization not relevant here.)
When I am running unit tests of the system I need to cause time to pass, preferably faster than normal. However, calling os.execute('sleep 1') consumes one wall clock second, but does not cause os.clock() to increment.
$ lua -e "require 'os' print(os.clock()) os.execute('sleep 1') print(os.clock())"
0.002493
0.002799
I can't use os.time() because this is only integer seconds (and less than that on systems compiled to use float instead double for numbers):
$ lua -e "require 'os' print(os.time()) os.execute('sleep 0.4') print(os.time())"
1397704209
1397704209
Can I force time to pass in my script without just busywaiting?

Answer 1

Paul answered this already: make os.clock return whatever you need.
I'm adding an implementation that lets you control how fast time passes according to os.clock \\\\\\\\\\\\\\\\\\\\\\\.
do
local realclock = os.clock
local lasttime = realclock()
local faketime = lasttime
local clockMultiplier = 1
function setClockMultiplier(multiplier)
clockMultiplier = multiplier
end
function adjustTime(offsetAmount)
faketime = faketime + offsetAmount
end
function os.clock()
local now = realclock()
adjustTime((now - lasttime) * clockMultiplier)
lasttime = now
return faketime
end
end
You can now call setClockMultiplier to freely slow down or speed up the passage of time as reported by os.clock. You can call adjustTime to advance or retard the clock by arbitrary amounts.

Answer 2

Why not write your own clock function that does what you want?
do
local clock = os.clock
local increment = 0
os.clock = function(inc)
increment = increment + (inc or 0)
return clock()+increment
end
end
print(os.clock())
os.clock(1)
print(os.clock())
This will print 0.001 1.001 or something similar.