mock introduction
Post on 08-Sep-2014
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Mock
Abstract
• Start to Write Test
• Start to Use Mock
• Tips
• You think quality is important
the first thing
• pip install nose
• you will get a tool called nosetests
A very simple test
def add(left,right): return left+right !
def test_add(): assert add(4,5) == 9
Finding, Running, Report in one shoot
nosetests sample.py
Ran 1 test in 0.001s !
OK
if you meet problem
def add(left,right): return left+right+1 !
def test_add(): assert add(4,5) == 9 !
trigger pdb as fail
nosetests sample_fail.py --pdb
assert add(4,5) == 9 (Pdb) p add(4,5) 10 (Pdb)
What nose do
• cooperate with doctest, unittest2
• add an additional function baed test case
• a test discover, test runner,
• plugin integration
unittest.TestCaseimport unittest !
def add(left,right): return left+right !
class addTestCase(unittest.TestCase): def test_add(self): self.assertEqual(5, add(5,5))
what else
• test fixture preparation
• setUP, tearDown
• setUp will be called before test method
• tearDown will be called after test method
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
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
all-mighty In : import mock !
In : m = mock.Mock() !
In : m.dock.dog.bark() Out: <Mock name='mock.dock.dog.bark()' id='4320364368'>
obey your orderIn: dog = mock.Mock( return_value="bark") !
In: dog() Out: ‘bark’ !
In: dog.bark.return_value = u"WW" !
In: dog.bark() Out: u'WW' !
mock tell you his storyIn [9]: def reset_file(fs): ...: fs.seek(0) ...: !
In: m = mock.Mock() !
In: reset_file(m) !
In: m.seek.assert_called_with(0)
like python objectIn : m = mock.MagicMock() !
In : m['key'] Out: <MagicMock name='mock.__getitem__()' id=‘4311227728'> !
In: m.__getitem__.return_value = 10 !
In: m[3] Out: 10 !
magic mock assertion
In: m.__getitem__.assert_called_with(3)
read specIn : fake_str = mock.Mock(str) !
In : fake_str.lower() Out: <Mock name='mock.lower()' id='4321150160'> !
In : fake_str.LOWER --------- AttributeError
General UsageIn : def count(fs): ...: return len(fs.read()) ...:In : fakefs = mock.Mock()
In : fakefs.read.return_value = "xx"
In : assert count(fakefs) == 2
Add Testability
• dependency should always pass from out side
• your design need to consider testability
Inversion of control
# not this def to_be_test(): db = Database() return db.all() !
# write this def to_be_test(db): return db.all()
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
Tips
• Q: How to maintain test case?
• refactor you test infrastructure often
• duplicated test code make you will feel tired after interface changed
• Q: how much should I test?
• test the interface, not the implementation
• don’t test private method
• test public method
• 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
Add test now
• My Project has no test …
• add test for new added code
• old code can add test latter
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
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
After we have tests
• don’t forget to run test before you push codes
• nose can provide report
• nose can integration coverage report
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
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