デコレータが邪魔してうまくテストできない例（mock 使えばいけるけど）

tests.py

# -*- coding: utf-8 -*-
import sys
import unittest


class WorkTest(unittest.TestCase):
    def _makeOne(self):
        from working import work
        return work

    def _callFUT(self, num):
        """Function Under Test."""
        func = self._makeOne()
        return func(num)

    def setUp(self):
        """Patch stdout."""
        import io
        self.default_out = sys.stdout
        self.dummy_out = io.StringIO()
        sys.stdout = self.dummy_out

    def tearDown(self):
        """Revert stdout."""
        sys.stdout = self.default_out

    def test_one(self):
        self._callFUT(3)

        self.dummy_out.seek(0)
        self.assertEqual(
            self.dummy_out.getvalue(),
            'ワイワイ！\nワイワイ！\nワイワイ！\n'
        )

if __name__ == '__main__':
    unittest.main()

working.py

# -*- coding: utf-8 -*-
from datetime import datetime


def teiji(hours, minutes):
    """定時出社チェック"""
    def _teiji(func):
        def wrapper(*args, **kwargs):
            now = datetime.now()
            teiji_date = datetime(
                now.year,
                now.month,
                now.day,
                hours,
                minutes
            )
            if now < teiji_date:
                func(*args, **kwargs)
            else:
                print('定時出社大失敗！')
        return wrapper
    return _teiji


@teiji(9, 0)
def work(num):
    for i in range(num):
        print('ワイワイ！')

if __name__ == '__main__':
    work(3)