I don't know of any QuickCheck library written particularly in or for CoffeeScript, but googling pulls up qc.js. Here's a snippet from demo.js in that repository:
declare("reverse", [arbWholeNumList, arbWholeNumList],
function(c, x, y) {
var z = x.concat(y);
x.reverse();
y.reverse();
z.reverse();
c.assert(z.toString() == y.concat(x).toString());
});
Now I'm no CoffeeScript expert, but I ran this through http://js2coffee.org. If you can manage to import qc.js, then using it from CoffeeScript would look something like this:
declare "reverse", [ arbWholeNumList, arbWholeNumList ], (c, x, y) ->
z = x.concat(y)
x.reverse()
y.reverse()
z.reverse()
c.assert z.toString() is y.concat(x).toString()