test the current OS
on mac:
var isOs = require('isos')
assert.ok(isOs('mac'))
assert.ok(isOs('darwin'))
assert.ok(isOs('osx'))
on windows:
var isOs = require('isos')
assert.ok(isOs('linux'))
on windows:
var isOs = require('isos')
assert.ok(isOs('windows'))
assert.ok(isOs('win32'))
etc...