現在時刻に依存したモジュールのテスト ref: http://qiita.com/ishiduca/items/f2ac1fbda6cfe8c236f4

result.txt

TAP version 13
# stub
# hook .toString
ok 1 (new Date).toSting() === "12"
ok 2 (new Date).toSting() === "hoge"
# reset .toString
ok 3 (new Date).toString() === "Sun Oct 06 2013 16:56:13 GMT+0900 (JST)"

1..3
# tests 3
# pass  3

# ok
ok      127 ms
All tests successful.
Files=1, Tests=3,  0 wallclock secs ( 0.06 usr  0.01 sys +  0.06 cusr  0.02 csys =  0.15 CPU)
Result: PASS

stub.js

var test = require('tape')

test('stub for Date#toString', function (t) {
    t.test('hook .toString', function (tt) {
        var stub = {}
        var toString

        function setup () {
            toString = Date.prototype.toString
            Date.prototype.toString = function () { return stub.time }
        }
        function teardown () {
            Date.prototype.toString = toString
            stub.time = null
        }
        function subtest (time) {
            stub.time = time
            tt.equal((new Date).toString(), time
              , '(new Date).toSting() === "' + time + '"')
        }

        setup()
        subtest(12)
        subtest('hoge')
        teardown()
        
        tt.end()
    })

    t.test('reset .toString', function (tt) {
        var d = new Date
        var str = d.toString()
        tt.ok(/\d\d:\d\d:\d\d\sGMT[+-]\d\d\d\d/.test(str)
          , '(new Date).toString() === "' + str + '"')
        tt.end()
    })

    t.end()
})