问题
I have a source code that opens a csv file and sets up a header to value association. The source code is given below:
def ParseCsvFile(source):
"""Parse the csv file.
Args:
source: file to be parsed
Returns: the list of dictionary entities; each dictionary contains
attribute to value mapping or its equivalent.
"""
global rack_file
rack_type_file = None
try:
rack_file = source
rack_type_file = open(rack_file) # Need to mock this line.
headers = rack_type_file.readline().split(',')
length = len(headers)
reader = csv.reader(rack_type_file, delimiter=',')
attributes_list=[] # list of dictionaries.
for line in reader:
# More process to happeng. Converting the rack name to sequence.
attributes_list.append(dict((headers[i],
line[i]) for i in range(length)))
return attributes_list
except IOError, (errno, strerror):
logging.error("I/O error(%s): %s" % (errno, strerror))
except IndexError, (errno, strerror):
logging.error('Index Error(%s), %s' %(errno, strerror))
finally:
rack_type_file.close()
I am trying to mock the following statement
rack_type_file = open(rack_file)
How do I mock open(...) function?
回答1:
This is admittedly an old question, hence some of the answers are outdated.
In the current version of the mock library there is a convenience function designed for precisely this purpose. Here's how it works:
>>> from mock import mock_open
>>> m = mock_open()
>>> with patch('__main__.open', m, create=True):
... with open('foo', 'w') as h:
... h.write('some stuff')
...
>>> m.mock_calls
[call('foo', 'w'),
call().__enter__(),
call().write('some stuff'),
call().__exit__(None, None, None)]
>>> m.assert_called_once_with('foo', 'w')
>>> handle = m()
>>> handle.write.assert_called_once_with('some stuff')
Documentation is here.
回答2:
To mock built-in function open with mox use __builtin__ module:
import __builtin__ # unlike __builtins__ this must be imported
m = mox.Mox()
m.StubOutWithMock(__builtin__, 'open')
open('ftphelp.yml', 'rb').AndReturn(StringIO("fake file content"))
m.ReplayAll()
# call the code you want to test that calls `open`
m.VerifyAll()
m.UnsetStubs()
Note that __builtins__ is not always a module, it can be of type dict, please use __builtin__ (with no "s") module to refer to system built-in methods.
More about __builtin__ module: http://docs.python.org/library/builtin.html
回答3:
There are two ways that I like to do this, depending on the situation.
If your unit test is going to call ParseCsvFile directly I would add a new kwarg to ParseCsvFile:
def ParseCsvFile(source, open=open):
# ...
rack_type_file = open(rack_file) # Need to mock this line.
Then your unit test can pass a different open_func in order to accomplish the mocking.
If your unit test calls some other function that in turn calls ParseCsvFile then passing around open_func just for tests is ugly. In that case I would use the mock module. This lets you alter a function by name and replace it with a Mock object.
# code.py
def open_func(name):
return open(name)
def ParseCsvFile(source):
# ...
rack_type_file = open_func(rack_file) # Need to mock this line.
# test.py
import unittest
import mock
from StringIO import StringIO
@mock.patch('code.open_func')
class ParseCsvTest(unittest.TestCase):
def test_parse(self, open_mock):
open_mock.return_value = StringIO("my,example,input")
# ...
回答4:
Is simple with decorator (Python3):
def my_method():
with open(file="/1.txt", mode='r', encoding='utf-8') as file:
return file.read().strip()
@mock.patch("builtins.open", create=True)
def test_my_method(mock_open):
mock_open.side_effect = [
mock.mock_open(read_data="A").return_value
]
resA = my_method()
assert resA == "A"
mock_open.mock_calls == [mock.call(file="/1.txt", mode='r', encoding='utf-8')]
回答5:
I took the liberty of re-writing your sample function:
Assume your function is located in a file named code.py
# code.py
import csv
import logging
def ParseCsvFile(source):
"""Parse the csv file.
Args:
source: file to be parsed
Returns: the list of dictionary entities; each dictionary contains
attribute to value mapping or its equivalent.
"""
global rack_file
rack_file = source
attributes_list = []
try:
rack_type_file = open(rack_file)
except IOError, (errno, strerror):
logging.error("I/O error(%s): %s", errno, strerror)
else:
reader = csv.DictReader(rack_type_file, delimiter=',')
attributes_list = [line for line in reader] # list of dictionaries
rack_type_file.close()
return attributes_list
A simple test case would be:
# your test file
import __builtin__
import unittest
import contextlib
from StringIO import StringIO
import mox
import code
@contextlib.contextmanager
def mox_replayer(mox_instance):
mox_instance.ReplayAll()
yield
mox_instance.VerifyAll()
class TestParseCSVFile(unittest.TestCase):
def setUp(self):
self.mox = mox.Mox()
def tearDown(self):
self.mox.UnsetStubs()
def test_parse_csv_file_returns_list_of_dicts(self):
TEST_FILE_NAME = 'foo.csv'
self.mox.StubOutWithMock(__builtin__, 'open')
open(TEST_FILE_NAME).AndReturn(StringIO("name,age\nfoo,13"))
with mox_replayer(self.mox):
result = code.ParseCsvFile(TEST_FILE_NAME)
self.assertEqual(result, [{'age': '13', 'name': 'foo'}]) # works!
if __name__ == '__main__':
unittest.main()
EDIT:
% /usr/bin/python2.6
Python 2.6.1 (r261:67515, Jun 24 2010, 21:47:49)
[GCC 4.2.1 (Apple Inc. build 5646)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import __builtin__
>>> import mox
>>> mock = mox.Mox()
>>> mock.StubOutWithMock(__builtin__, 'open')
>>> mock.UnsetStubs()
Works fine on 2.6 using mox 0.53
回答6:
Hi I was having a similar problem, and was tearing my hair out flipping between different mocking libraries. I finally found a solution that I am happy with, and maybe it might help you? In the end I went with the Mocker library http://labix.org/mocker and here is the code for mocking open:
from mocker import Mocker
from StringIO import StringIO
import __builtin__
mocker = Mocker()
sourceFile = 'myTestFile.txt'
__builtin__.open = mocker.mock()
__builtin__.open(sourceFile)
mocker.result(StringIO('this,is,a,test,file'))
<the rest of your test setup goes here>
mocker.replay()
ParseCsvFile(sourceFile)
mocker.restore()
mocker.verify()
Incidentaly the reason I went with Mocker is because I was testing a function which used open to read a file, and then used open again to overwrite the same file with new data. What I needed to be able to do was test the case where the initial file didn't exist, so set up a mock, that threw an IOError the first time, and then worked the second time. The setup for which looked like this:
from mocker import Mocker
import __builtin__
mocker = Mocker()
mockFileObject = mocker.mock()
__builtin__.open = mocker.mock()
__builtin__.open('previousState.pkl', 'r')
mocker.throw(IOError('Boom'))
__builtin__.open('previousState.pkl','w')
mocker.result(mockFileObject)
<rest of test setup >
mocker.replay()
<test>
mocker.restore() #required to restore the open method
mocker.verify()
Hope this helps!
回答7:
@mock.patch decorator (2.7 example)
This is now much easier:
import your_script.py
import __builtin__
import mock
@mock.patch("__builtin__.open")
def test_example(self, mock_open):
your_script.your_method()
self.assertEqual(mock_open.call_count, 1)
回答8:
>>> class A(object):
... def __init__(self):
... self.x = open('test.py')
...
>>> old_open = open
>>> def open(s):
... return "test\n"
...
>>> a = A()
>>> a.x
'test\n'
>>> open = old_open
>>> a = A()
>>> a.x
<open file 'test.py', mode 'r' at 0xb7736230>
来源：https://stackoverflow.com/questions/5237693/mocking-openfile-name-in-unit-tests