Cleaner unit testing with the Arrange Act Assert pattern

My name is James and I've been using the Arrange Act Assert pattern as part of my daily Test Driven Development practice for a number of years over multiple projects with different development teams. During this time I've worked to make my tests as readable, simple and generally Pythonic as possible - and I firmly believe that the AAA pattern can help us all with this quest.

See my blog post for more info: http://jamescooke.info/cleaner-unit-testing-with-the-arrange-act-assert-pattern.html

Transcript

1. Cleaner unit testing with the
   Arrange
   Act
   Assert
   pattern
   James Cooke
   Licensed under the
   Creative Commons Attribution-ShareAlike 3.0 Unported License.
   

   View Slide

2. Outline
   ●
   Background
   ●
   Problem
   ●
   AAA pattern
   ●
   Smells and solutions
   ●
   Questions in the break
   

   View Slide

3. Background
   ●
   Python developer
   ●
   TDD with AAA
   ●
   github.com/txels
   

   View Slide

4. Givens
   ●
   PEP008 is beneficial
   ●
   PEP020 is our mantra
   ●
   We all TDD
   ●
   Every test is a function, uncoupled
   ●
   Simplicity trumps performance
   ●
   Eliminate duplication
   

   View Slide

5. Problem
   ●
   Pythonic code in project, carnage
   in tests
   ●
   Tests of OSS projects are often
   hard to understand
   ●
   Tests are non-uniform
   

   View Slide

6. Example
   Member
   Account
   Membership
   1 1
   m m
   

   View Slide

7. The Pattern
   def test_x(*args, **kwargs):
   """__docstring__
   """
   # Arrange
   # Act
   # Assert
   AKA ‘AAA’ or ‘3A’
   

   View Slide

8. def test_x(*args, **kwargs):
   """__docstring__
   """
   # Arrange
   # Act
   # Assert
   

   View Slide

9. def test_printable_name():
   """__docstring__
   """
   # Arrange
   # Act
   # Assert
   

   View Slide

10. Docstring
    ●
    Follow existing style of your
    project
    ●
    First line positive statement of
    tested action
    ●
    Extra info about test, conditions
    

    View Slide

11. def test_printable_name():
    """__docstring__
    """
    # Arrange
    # Act
    # Assert
    

    View Slide

12. def test_printable_name():
    """New members have printable names
    """
    # Arrange
    # Act
    # Assert
    

    View Slide

13. Arrange
    ●
    Single block of code
    ●
    No assertions
    ●
    Only prepare non-deterministic
    results not available after Act
    ●
    Should not require comments
    

    View Slide

14. def test_printable_name():
    """New members have printable names
    """
    # Arrange
    # Act
    # Assert
    

    View Slide

15. def test_printable_name():
    """New members have printable names
    """
    person = Member()
    person.first_name = 'René'
    person.last_name = ' 北京 '
    # Act
    # Assert
    

    View Slide

16. Act
    ●
    `result = ` format
    ●
    One line only
    ●
    Can be wrapped in `with
    raises` for expected exceptions
    

    View Slide

17. def test_printable_name():
    """New members have printable names
    """
    person = Member()
    person.first_name = 'René'
    person.last_name = ' 北京 '
    # Act
    # Assert
    

    View Slide

18. def test_printable_name():
    """New members have printable names
    """
    person = Member()
    person.first_name = 'René'
    person.last_name = ' 北京 '
    result = person.printable_name()
    # Assert
    

    View Slide

19. Assert
    ●
    Single block of code
    ●
    No actions should happen
    ●
    Test result first, then side effects
    ●
    Use simple blocks of assertions
    

    View Slide

20. def test_printable_name():
    """New members have printable names
    """
    person = Member()
    person.first_name = 'René'
    person.last_name = ' 北京 '
    result = person.printable_name()
    # Assert
    

    View Slide

21. def test_printable_name():
    """New members have printable names
    """
    person = Member()
    person.first_name = 'René'
    person.last_name = ' 北京 '
    result = person.printable_name()
    assert result == ' 北京 , René'
    

    View Slide

22. Smell: Assertions in Arrange
    

    View Slide

23. def test_account_list():
    """Member can list their accounts
    """
    person = Member()
    account = Account()
    person.join(account)
    assert person in account.members
    result = person.account_list()
    assert len(result) == 1
    assert account in result
    

    View Slide

24. person = Member()
    account = Account()
    person.join(account)
    assert person in account.members
    

    View Slide

25. person = Member()
    account = Account()
    person.join(account)
    result = account.members
    assert person in account.members
    

    View Slide

26. person = Member()
    account = Account()
    person.join(account)
    result = account.members
    assert person in result
    

    View Slide

27. def test_account_member():
    """Member can join account
    """
    person = Member()
    account = Account()
    person.join(account)
    result = account.members
    assert person in result
    

    View Slide

28. def test_account_member():
    """Member can join account
    """
    person = Member()
    account = Account()
    person.join(account)
    result = account.members
    assert person in result
    def test_account_list():
    """Member can list their accounts
    """
    person = Member()
    account = Account()
    person.join(account)
    assert person in account.members
    result = person.account_list()
    assert len(result) == 1
    assert account in result
    

    View Slide

29. def test_account_member():
    """Member can join account
    """
    person = Member()
    account = Account()
    person.join(account)
    result = account.members
    assert person in result
    def test_account_list():
    """Member can list their accounts
    """
    person = Member()
    account = Account()
    person.join(account)
    result = person.account_list()
    assert len(result) == 1
    assert account in result
    ●
    Eliminate duplication
    

    View Slide

30. def test_account_member():
    """Member can join account
    """
    person = Member()
    account = Account()
    person.join(account)
    result = account.members
    assert person in result
    def test_account_list():
    """Member can list their accounts
    """
    person = Member()
    account = Account()
    person.join(account)
    result = person.account_list()
    assert len(result) == 1
    assert account in result
    person = Member()
    account = Account()
    person.join(account)
    return person, account
    

    View Slide

31. def test_account_member():
    """Member can join account
    """
    person = Member()
    account = Account()
    person.join(account)
    result = account.members
    assert person in result
    def test_account_list():
    """Member can list their accounts
    """
    person = Member()
    account = Account()
    person.join(account)
    result = person.account_list()
    assert len(result) == 1
    assert account in result
    def account_member_factory():
    """Create Member and Account pair
    """
    person = Member()
    account = Account()
    person.join(account)
    return person, account
    

    View Slide

32. def account_member_factory():
    """Create Member and Account pair
    """
    person = Member()
    account = Account()
    person.join(account)
    return person, account
    def test_account_member():
    """Member can join account
    """
    person = Member()
    account = Account()
    person.join(account)
    result = account.members
    assert person in result
    def test_account_list():
    """Member can list their accounts
    """
    person = Member()
    account = Account()
    person.join(account)
    result = person.account_list()
    assert len(result) == 1
    assert account in result
    

    View Slide

33. def account_member_factory():
    """Create Member and Account pair
    """
    person = Member()
    account = Account()
    person.join(account)
    return person, account
    def test_account_list():
    """Member can list their accounts
    """
    person = Member()
    account = Account()
    person.join(account)
    result = person.account_list()
    assert len(result) == 1
    assert account in result
    def test_account_member():
    """Member can join account
    """
    person, account = account_member_factory()
    result = account.members
    assert person in result
    

    View Slide

34. def account_member_factory():
    """Create Member and Account pair
    """
    person = Member()
    account = Account()
    person.join(account)
    return person, account
    def test_account_member():
    """Member can join account
    """
    person, account = account_member_factory()
    result = account.members
    assert person in result
    def test_account_list():
    """Member can list their accounts
    """
    person, account = account_member_factory()
    result = person.account_list()
    assert len(result) == 1
    assert account in result
    

    View Slide

35. def account_member_factory():
    """Create Member and Account pair
    """
    person = Member()
    account = Account()
    person.join(account)
    return person, account
    def test_account_member_factory():
    """Member can join account
    """
    person, account = account_member_factory()
    result = account.members
    assert person in result
    def test_account_list():
    """Member can list their accounts
    """
    person, account = account_member_factory()
    result = person.account_list()
    assert len(result) == 1
    assert account in result
    

    View Slide

36. def account_member_factory():
    """Create Member and Account pair
    """
    person = Member()
    account = Account()
    person.join(account)
    return person, account
    def test_account_member_factory():
    """account_member_factory creates joined Member Account pair
    """
    person, account = account_member_factory()
    result = account.members
    assert person in result
    def test_account_list():
    """Member can list their accounts
    """
    person, account = account_member_factory()
    result = person.account_list()
    assert len(result) == 1
    assert account in result
    

    View Slide

37. Smell: Duplication between
    tests
    

    View Slide

38. Example
    Member A
    Account 1
    Member B
    Member C
    Account 2
    Account 3
    

    View Slide

39. def test_a_transfer_b():
    """Member A in Account 1 can transfer to B
    """
    user_a, account_one = account_member_factory()
    user_b, account_two = account_member_factory()
    user_b.join(account_one)
    user_c, account_three = account_member_factory()
    # Act
    # Assert
    def test_a_not_transfer_c():
    """Member A in Account 1 can not tranfer to C
    """
    user_a, account_one = account_member_factory()
    user_b, account_two = account_member_factory()
    user_b.join(account_one)
    user_c, account_three = account_member_factory()
    # Act
    # Assert
    def test_c_not_transfer_a():
    """Member C in Account 3 can not tranfer to A
    """
    user_a, account_one = account_member_factory()
    user_b, account_two = account_member_factory()
    ●
    Eliminate duplication
    

    View Slide

40. class TestTranfers(unittest.TestCase):
    def test_a_transfer_b():
    """Member A in Account 1 can transfer to B
    """
    user_a, account_one = account_member_factory()
    user_b, account_two = account_member_factory()
    user_b.join(account_one)
    user_c, account_three = account_member_factory()
    # Act
    # Assert
    def test_a_not_transfer_c():
    """Member A in Account 1 can not tranfer to C
    """
    user_a, account_one = account_member_factory()
    user_b, account_two = account_member_factory()
    user_b.join(account_one)
    user_c, account_three = account_member_factory()
    # Act
    # Assert
    def test_c_not_transfer_a():
    """Member C in Account 3 can not tranfer to A
    """
    user_a, account_one = account_member_factory()
    user_b, account_two = account_member_factory()
    

    View Slide

41. class TestTranfers(unittest.TestCase):
    def test_a_transfer_b(self):
    """Member A in Account 1 can transfer to B
    """
    user_a, account_one = account_member_factory()
    user_b, account_two = account_member_factory()
    user_b.join(account_one)
    user_c, account_three = account_member_factory()
    # Act
    # Assert
    def test_a_not_transfer_c(self):
    """Member A in Account 1 can not tranfer to C
    """
    user_a, account_one = account_member_factory()
    user_b, account_two = account_member_factory()
    user_b.join(account_one)
    user_c, account_three = account_member_factory()
    # Act
    # Assert
    def test_c_not_transfer_a(self):
    """Member C in Account 3 can not tranfer to A
    """
    user_a, account_one = account_member_factory()
    user_b, account_two = account_member_factory()
    

    View Slide

42. class TestTranfers(unittest.TestCase):
    def setUp(self):
    """
    """
    def test_a_transfer_b(self):
    """Member A in Account 1 can transfer to B
    """
    user_a, account_one = account_member_factory()
    user_b, account_two = account_member_factory()
    user_b.join(account_one)
    user_c, account_three = account_member_factory()
    # Act
    # Assert
    

    View Slide

43. Addendum: TestCase.setUp
    ●
    A pure Arrange block
    ●
    Docstring if required
    ●
    Assert valid with a special test
    called test_set_up
    

    View Slide

44. class TestTranfers(unittest.TestCase):
    def setUp(self):
    """Create three Accounts and three members
    --------+---------------------------
    Member | Accounts
    --------+---------------------------
    user_a | account_one
    user_b | account_one, account_two
    user_c | account_three
    --------+---------------------------
    """
    super().setUp()
    self.user_a, self.account_one = account_member_factory()
    self.user_b, self.account_two = account_member_factory()
    self.user_b.join(self.account_one)
    self.user_c, self.account_three = account_member_factory()
    def test_a_transfer_b(self):
    """Member A in Account 1 can transfer to B
    """
    user_a, account_one = account_member_factory()
    user_b, account_two = account_member_factory()
    user_b.join(account_one)
    user_c, account_three = account_member_factory()
    # Act
    # Assert
    

    View Slide

45. class TestTranfers(unittest.TestCase):
    def setUp(self):
    """Create three Accounts and three members
    --------+---------------------------
    Member | Accounts
    --------+---------------------------
    user_a | account_one
    user_b | account_one, account_two
    user_c | account_three
    --------+---------------------------
    """
    super().setUp()
    self.user_a, self.account_one = account_member_factory()
    self.user_b, self.account_two = account_member_factory()
    self.user_b.join(self.account_one)
    self.user_c, self.account_three = account_member_factory()
    def test_a_transfer_b(self):
    """Member A in Account 1 can transfer to B
    """
    # Act
    # Assert
    def test_a_not_transfer_c(self):
    """Member A in Account 1 can not tranfer to C
    """
    # Act
    

    View Slide

46. class TestTranfers(unittest.TestCase):
    def setUp(self):
    """Create three Accounts and three members
    --------+---------------------------
    Member | Accounts
    --------+---------------------------
    user_a | account_one
    user_b | account_one, account_two
    user_c | account_three
    --------+---------------------------
    """
    super().setUp()
    self.user_a, self.account_one = account_member_factory()
    self.user_b, self.account_two = account_member_factory()
    self.user_b.join(self.account_one)
    self.user_c, self.account_three = account_member_factory()
    def test_set_up(self):
    def test_a_transfer_b(self):
    """Member A in Account 1 can transfer to B
    """
    # Act
    # Assert
    

    View Slide

47. Addendum: test_set_up
    ●
    A pure Assert block
    ●
    Docstring if required
    

    View Slide

48. class TestTranfers(unittest.TestCase):
    def setUp(self):
    """Create three Accounts and three members
    --------+---------------------------
    Member | Accounts
    --------+---------------------------
    user_a | account_one
    user_b | account_one, account_two
    user_c | account_three
    --------+---------------------------
    """
    super().setUp()
    self.user_a, self.account_one = account_member_factory()
    self.user_b, self.account_two = account_member_factory()
    self.user_b.join(self.account_one)
    self.user_c, self.account_three = account_member_factory()
    def test_set_up(self):
    assert self.user_a.account_list() == [self.account_one]
    assert self.user_b.account_list() == [self.account_one, self.account_two
    assert self.user_c.account_list() == [self.account_three]
    def test_a_transfer_b(self):
    """Member A in Account 1 can transfer to B
    """
    # Act
    # Assert
    

    View Slide

49. class TestTranfers(unittest.TestCase):
    def setUp(self):
    """Create three Accounts and three members
    --------+---------------------------
    Member | Accounts
    --------+---------------------------
    user_a | account_one
    user_b | account_one, account_two
    user_c | account_three
    --------+---------------------------
    """
    super().setUp()
    self.user_a, self.account_one = account_member_factory()
    self.user_b, self.account_two = account_member_factory()
    self.user_b.join(self.account_one)
    self.user_c, self.account_three = account_member_factory()
    def test_set_up(self):
    assert self.user_a.account_list() == [self.account_one]
    assert self.user_b.account_list() == [self.account_one, self.account_two]
    assert self.user_c.account_list() == [self.account_three]
    def test_a_transfer_b(self):
    """Member A in Account 1 can transfer to B
    """
    # Act
    # Assert
    def test_a_not_transfer_c(self):
    """Member A in Account 1 can not tranfer to C
    """
    # Act
    # Assert
    def test_c_not_transfer_a(self):
    """Member C in Account 3 can not tranfer to A
    """
    # Act
    # Assert
    

    View Slide

50. Summary
    ●
    Demonstrated AAA
    ●
    Small and simple tests
    ●
    Opens the door to DRY and clarity
    

    View Slide

51. Thanks!
    ●
    Resources:
    http://jamescooke.info/cleaner...
    ●
    @jamesfublo
    ●
    Come ask questions
    ●
    Let’s talk more about testing
    ●
    Thanks for listening!
    Licensed under the
    Creative Commons Attribution-ShareAlike 3.0 Unported License.
    

    View Slide