Please show the canonical way to switch between test and production

[pytest-dev]

Please show the canonical way to switch between test and production

[GoogleCodeExporter]

Fair enough. Unfortunately, the Testing on the Toilet won't be very helpful, 
since the examples rely on internal modules. What I can do is show how to use 
pyfakefs with unittest. Your production code remains untouched in your 
production modules, and the _test.py files with your unit test will mock the os 
module in your production module with pyfakefs. No changes are required to your 
production module.

The following is untested:

import unittest
import fake_filesystem
import yourmodule

class GroupOfTests(unittest.TestCase):
  def setUp(self):
    self.stubs = unittest.StubOutForTesting()

    # this fakes the os and os.path modules
    self.fs = fake_filesystem.FakeFilesystem()
    self.os = fake_filesystem.FakeOsModule(self.fs)
    self.stubs.SmartSet(yourmodule, 'os', self.os)

    # this redirects any open() for file() calls to the fake filesystem
    self.fake_open = fake_filesystem.FakeFileOpen(self.fs)
    self.stubs.SmartSet(__builtins__, 'file', self.fake_open)
    self.stubs.SmartSet(__builtins__, 'open', self.fake_open)

    # in tests, manipulate the fake filesystem through the
    # FakeFilesystem() object
    self.fs.CreateDirectory('/adir')
    self.fs.CreateFile('/adir/afile', contents='what ever')

  def tearDown(self):
    self.stubs.SmartUnsetAll()

  def testSomething(self):
    # test the fake filesystem through the FakeFilesystem() object
    self.assertTrue(self.fs.Exists('/adir/afile'))

Original comment by [email protected] on 1 Oct 2013 at 11:34

• Changed state: Started

[GoogleCodeExporter]

Ah.  unittest.StubOutForTesting().  After I get this going, I'll try to get 
back to write up a wiki article for you.

Thank you for your quick and complete response.

Original comment by [email protected] on 1 Oct 2013 at 11:45

[GoogleCodeExporter]

Now I am looking at refining (and publishing) this approach.

I have a question that is a matter of style.  Your example depends on the mox 
module because it uses mox.stubout.StubOutForTesting.  Should the published, 
"canonical" solution use mox, or should I switch to some other module like 
stub? 

Original comment by [email protected] on 14 Jan 2014 at 7:45

[GoogleCodeExporter]

mox.stubout will work. Basically, something needs to manage the stub, even if 
it is just part of the test:

def setUp(self):
  self._save_file = __builtins__.file
  self._save_open = __builtins__.open
  __builtins__.file = self.fake_open
  __builtins__.open = self.fake_open

def tearDown(self):
  __builtins__.file = self._save_file
  __builtins__.open = self._save_open

Original comment by [email protected] on 14 Jan 2014 at 8:35

[GoogleCodeExporter]

Okay, I'll stick with mox for now.

Original comment by [email protected] on 14 Jan 2014 at 9:15

[GoogleCodeExporter]

I have a new base class pyfakefs.fake_filesystem_unittest.TestCase.  When you 
replace unittest.TestCase with this, it causes the fake filesystem to be used 
by all the tests and the software under test.

I also created an example module and a test for it.  This demonstrates how to 
use pyfakefs.fake_filesystem_unittest.TestCase.

I would like to push this code for you to scrutinize, and I would like to write 
a "Getting Started" wiki article.

I do not see any "pull request" functionality on Google Code.  How can we 
proceed?

Original comment by [email protected] on 16 Jan 2014 at 2:26

Attachments:

• fake_filesystem_unittest.py
• fake_filesystem_unittest_test.py
• example.py
• example_test.py

[GoogleCodeExporter]

I have a solution for doctest, too.  Are you interested?

Original comment by [email protected] on 23 Jan 2014 at 5:31

[GoogleCodeExporter]

See https://code.google.com/r/jmcgeheeiv-pyfakefs/ for code that supports both 
unittest and doctest, plus a practical example and tutorial. 

Original comment by [email protected] on 9 May 2014 at 6:28

[jmcgeheeiv]

Upon moving this project from Google Code to GitHub project jmcgeheeiv/pyfakefs, I merged the jmcgeheeiv-pyfakefs files, and edited the usage tutorial into the wiki.