Mock Introduction

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I introduce the python mock library in Taipei.py http://meetup.com/Taipei-py/

I introduce the python mock library in Taipei.py http://meetup.com/Taipei-py/

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Transcript

  • 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