2

3

1

Добавяме тест за несъществуващ код

import unittest                                      #test.py

class Test(unittest.TestCase):

    def test_str(self):
        self.assertEqual(to_digits(123456), [1,2,3,4,5,6])

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

$ python3 test.py 
E
======================================================================
ERROR: test_str (__main__.Test)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "test.py", line 6, in test_str
    self.assertEqual(to_digits(123456), [1,2,3,4,5,6])
NameError: name 'to_digits' is not defined

----------------------------------------------------------------------
Ran 1 test in 0.000s

FAILED (errors=1)

3

def to_digits(digits):
    result = []

    for n in str(digits):
        result.append(int(n))

    return result

2

Пишем код, колкото теста да мине

$ python3 test.py 
.
----------------------------------------------------------------------
Ran 1 test in 0.000s

OK

def to_digits(digits):
    return [int(x) for x in str(digits)]

Refactoring

$ python3 test.py 
.
----------------------------------------------------------------------
Ran 1 test in 0.000s

OK

import unittest
from implementation import to_digits

class Test(unittest.TestCase):

    def test_str(self):
        self.assertEqual(to_digits(123456), [1,2,3,4,5,6])
        self.assertEqual(to_digits(999), [9, 9, 9])

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

Относно refactoring-a