notebook.community

Edit and run



In [ ]:

    
# EXERCISE:
# Execute nosetests in this folder:
!nosetests -sv
# Exercise: review tests_lib and make the tests to pass
# Use this cell

Regarding mocking, in Python monkey patching classes is trivial. It is really easy to replace instances methods or modules functions with your own stuff.
To use real full-featured mocks use the 'mock' library:
- http://www.voidspace.org.uk/python/mock/
- It was added to Python standard library in 3.3 as 'unittest.mock'
  - http://docs.python.org/3/library/unittest.mock.html
mock library allows to replace parts of our code in a safe and easy way with
- mock objects. You can assert how they are called too.
Base class is Mock although is advisable to use MagicMock subclass
- MagicMock has all "magic" methods already pre-created
patch utility allow to monkey patching at module and class level within the scope of test
Let's see a quick example



In [ ]:

    
from mock import MagicMock
from lib_to_test import ProductionClass



In [ ]:

    
from mock import MagicMock
from lib_to_test import ProductionClass
prod = ProductionClass()
prod.prod_method = MagicMock(return_value=3)
print prod.prod_method(40, 3)
prod.prod_method.assert_called_once_with(40, 3)



In [ ]:

    
# with side_effect we can return several values and raise exceptions too
prod.prod_method = MagicMock(side_effect=ValueError("not number"))
prod.prod_method("my_string")



In [ ]:

    
prod.prod_method = MagicMock(side_effect=[2, 3, 4])
prod.prod_method(34, 2)
prod.prod_method(34, 2)
prod.prod_method(34, 2)



In [ ]:

    
# But we are modifying our source code, we better use patch
from mock import patch



In [ ]:

    
import lib_to_test
# patch as decorator, provides MagicMock in function decorated
@patch('lib_to_test.ProductionClass')
def test(mockClass):
    lib_to_test.ProductionClass()  # Already imported in module..
    print 'ProductionClass {}'.format(lib_to_test.ProductionClass)
    assert mockClass is lib_to_test.ProductionClass
    print mockClass.called



In [ ]:

    
test()



In [ ]:

    
print lib_to_test.ProductionClass



In [ ]:

    
# We can also use patch for system libraries...
import sys

# patch as context manager
with patch('sys.exit') as exitMock:
    try:
        sys.exit()
    except SystemExit:
        print "exiting programm"
    exitMock.assert_called_once_with()



In [ ]:

    
try:
    sys.exit()
except SystemExit:
    print "exiting programm"



In [ ]:

    
# we can patch some object, dict, open and magic methods....

my_patch = patch.object(prod, 'prod_method')
method_mock = my_patch.start()
method_mock.return_value = 5000
print prod.prod_method(30, 3)



In [ ]:

    
# we stop the patch now ...
my_patch.stop()
print prod.prod_method
print prod.prod_method(30, 3)



In [ ]:

    
# WTF ??, yes before we change ProductionClass inside the module....
print prod.prod_method
prod = ProductionClass()
my_patch = patch.object(prod, 'prod_method')
method_mock = my_patch.start()
method_mock.return_value = 5000
print prod.prod_method(30, 3)
my_patch.stop()
print prod.prod_method(30, 3)



In [ ]:

    
# magic methods
mock = MagicMock()
mock.__str__.return_value = 'foobarbaz'
cad = str(mock)
mock.__str__.assert_called_with()
print cad



In [ ]:

    
# dictionary
foo = {'key': 'value'}
original = foo.copy()
with patch.dict(foo, {'newkey': 'newvalue'}, clear=True):
    print "dict foo is now: {}".format(foo)
    assert foo == {'newkey': 'newvalue'}



In [ ]:

    
print "dict foo is {}".format(foo)
assert foo == original



In [ ]:

    
# open function can be patched tooo....
from mock import mock_open

# write
with patch('__builtin__.open', mock_open()) as m:
    with open('foo.txt', 'w') as f:
        f.write('something')
    print m.mock_calls



In [ ]:

    
import os
os.path.exists('foo.txt')



In [ ]:

    
# read
with patch('__builtin__.open', mock_open( read_data='foo')) as m:
    with open('foo.txt') as f:
        file = f.read()
    print file



In [ ]:

    
!pip install nose-cov
!nosetests -s -v --with-cover --cover-package=lib_to_test

SOURCES: