Unit vs Integration testing in python using mocks

adrian.py

# consider this simple password hasher (over-simplified of course):

def password_hash(self, salt, password):
  return (salt + password).reverse

# the unit tests are simple input vs output style:

def test_password_hash_returns_reverse_concatenated_salt_and_password(self):
  hashed = password_hash('foo', 'bar')
  self.assertEqual(hashed, 'raboof')

# now consider this more complicated example that interacts with user objects and hasing functions:

class UserPasswordHasher:
  def __init__(self, user, hasher=sha123):
    self.user = user
    self.hasher = hasher
  
  def salted_hash(self, password):
    return self.hasher(self.user.email + password)

# the unit tests verify interaction with other units using mock objects:
# (Mock()s are special objects that let you fake and verify attributes/calls)

class TestUserPasswordHasher(TestCase):
  def setUp(self):
    fake_user = Mock(email='[email protected]')
    self.fake_hasher = Mock()
    user_password_hasher = UserPasswordHasher(fake_user, self.fake_hasher)
    self.salted_hash = user_password_hasher.salted_hash('password')
  
  def test_salted_hash_returns_results_of_hasher(self):
    self.assertEqual(self.salted_hash, self.fake_hasher.return_value)
  
  def test_salted_hash_salts_password_with_user_email(self):
    self.fake_hasher.assert_called_with('[email protected]')

# the integration tests verify the behavior when the real units are interacting with each other:

class TestUserPasswordHasher(TestCase):
  def test_returns_same_hash_for_same_user_and_password(self):
    user = User()
    hash1 = UserPasswordHasher(user).salted_hash('password')
    hash2 = UserPasswordHasher(user).salted_hash('password')
    self.assertEqual(hash1, hash2)
  
  def test_returns_different_hash_for_same_user_with_different_passwords(self):
    user = User()
    hash1 = UserPasswordHasher(user).salted_hash('password1')
    hash2 = UserPasswordHasher(user).salted_hash('password2')
    self.assertNotEqual(hash1, hash2)

  def test_returns_different_hash_for_different_user_with_same_passwords(self):
    user1 = User(email='[email protected]')
    user2 = User(email='[email protected]')
    hash1 = UserPasswordHasher(user1).salted_hash('password')
    hash2 = UserPasswordHasher(user2).salted_hash('password')
    self.assertNotEqual(hash1, hash2)