This document provides an introduction to unit testing in Python using the nose testing framework and mock library. It discusses: 1) How to install and use nose to find, run tests, and generate reports in one step. Nose can integrate with doctests and unittest. 2) The basics of writing unit tests using assert statements and examples of simple passing and failing tests. 3) How to use the mock library to fake dependencies in tests by mocking objects and specifying return values. This improves test isolation and speed. 4) Best practices for test-driven development including writing quick and focused tests, mocking time-consuming objects, and only running failed tests when issues are encountered. Dependency injection and inversion of

1. Mock

2. Abstract
• Start to Write Test
• Start to Use Mock
• Tips

3. • You think quality is
important

4. the first thing
• pip install nose
• you will get a tool called nosetests

5. A very simple test
def add(left,right):
return left+right
!
def test_add():
assert add(4,5) == 9

6. Finding, Running, Report in
one shoot
nosetests sample.py
Ran 1 test in 0.001s
!
OK

7. if you meet problem
def add(left,right):
return left+right+1
!
def test_add():
assert add(4,5) == 9
!

8. trigger pdb as fail
nosetests sample_fail.py --pdb
assert add(4,5) == 9
(Pdb) p add(4,5)
10
(Pdb)

9. What nose do
• cooperate with doctest, unittest2
• add an additional function baed test case
• a test discover, test runner,
• plugin integration

10. unittest.TestCase
import unittest
!
def add(left,right):
return left+right
!
class addTestCase(unittest.TestCase):
def test_add(self):
self.assertEqual(5, add(5,5))

11. what else
• test fixture preparation
• setUP, tearDown
• setUp will be called before test method
• tearDown will be called after test method

12. what if
• if a function called erase_disk , how can I test
it?
• if a function will get a JSON from google, how
can I test it

13. Time to Introduce Mock
• python3.3 builtin
• pip install mock with python2.7
• it is a library
• it helps you to provide a fake object for spy

14. all-mighty
In : import mock
!
In : m = mock.Mock()
!
In : m.dock.dog.bark()
Out: <Mock
name='mock.dock.dog.bark()'
id='4320364368'>

15. obey your order
In: dog = mock.Mock(
return_value="bark")
!
In: dog()
Out: ‘bark’
!
In: dog.bark.return_value = u"WW"
!
In: dog.bark()
Out: u'WW'
!

16. mock tell you his story
In [9]: def reset_file(fs):
...: fs.seek(0)
...:!
In: m = mock.Mock()
!
In: reset_file(m)
!
In: m.seek.assert_called_with(0)

17. like python object
In : m = mock.MagicMock()
!
In : m['key']
Out: <MagicMock
name='mock.__getitem__()'
id=‘4311227728'>
!
In: m.__getitem__.return_value = 10
!
In: m[3]
Out: 10

18. magic mock assertion
In:
m.__getitem__.assert_called_with(3)

19. read spec
In : fake_str = mock.Mock(str)
!
In : fake_str.lower()
Out: <Mock name='mock.lower()'
id='4321150160'>
!
In : fake_str.LOWER
---------
AttributeError

20. General Usage
In : def count(fs):
...: return len(fs.read())
...:
In : fakefs = mock.Mock()
In : fakefs.read.return_value = "xx"
In : assert count(fakefs) == 2

21. Add Testability
• dependency should always pass from out side
• your design need to consider testability

22. Inversion of control
# not this
def to_be_test():
db = Database()
return db.all()
!
# write this
def to_be_test(db):
return db.all()

23. from mock import *
from StringIO import *
def do_print(): # hard to IoC
print "hi"
def test_print():
os = StringIO()
with patch('sys.stdout',
new=os):
do_print()
actual = os.getvalue()
expect = "hi"
assert expect in actual

24. Tips
• Q: How to maintain test case?
• refactor you test infrastructure often
• duplicated test code make you will feel tired
after interface changed

25. • Q: how much should I test?
• test the interface, not the implementation
• don’t test private method
• test public method

26. • Q: Test is slow, I don’t want to test
• write quick test
• mock time consuming object
• don’t execute time consuming test every time
• run failed test only while you meet error

27. Add test now
• My Project has no test …
• add test for new added code
• old code can add test latter

28. mock needs manage
• Mock is awesome, I want to mock every thing
• mock’s behavior may has error
• mock object tell you what you want to hear
• mock dependency is okay
• share mock among test modules

29. finding test utility
• Django mocks some service while testing
• GAE also provide mock while testing
• if you are using ORM, there a package that help
you mock ORM

30. After we have tests
• don’t forget to run test before you push codes
• nose can provide report
• nose can integration coverage report

31. Recap
• Nose is a good test driver
• unittest provide awesome test infrastructure
• any one want to share doctest?
• test and doc are combined !
• mock is used to fake a dependency, not every
thing