variable_test.py

import unittest

class User:
    number = 1
    articles = []

    # def __init__(self):
    #     self.number = 1
    #     self.articles = []

    def write(self, text):
        self.articles.append(text)

class UserTest(unittest.TestCase):

    def test(self):
        user1 = User()
        user2 = User()

        self.assertEqual(User.number, 1)
        self.assertEqual(user1.number, 1)
        user1.number = 2
        self.assertEqual(User.number, 1)
        User.number = 3
        self.assertEqual(User.number, 3)
        self.assertEqual(user1.number, 2)
        self.assertEqual(user2.number, 3)

        user1.write('a')
        user1.write('b')
        self.assertEqual(user1.articles, ['a', 'b',])

        self.assertEqual(user2.articles, ['a', 'b',])
        user2.write('c')
        user2.write('d')
        self.assertEqual(user2.articles, ['a', 'b', 'c', 'd',])

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