Added pytest plugin support

[wesleykendall]

Hello, I love this library and would really like to use it as a pytest fixture in my tests without having to define it myself. This PR adds a pytest plugin as part of the installation for pyfakefs. In other words, installing pyfakefs allows one to do:

def my_fake_fs_test(fs):
  fs.CreateFile('/var/data/xx1.txt', contents='Hello!')
  assert os.path.exists('/var/data/xx1.txt')

I used your example in conftest.py, along with returning the fs attribute of the created Patcher object. Everything works so far in my fakefs tests.

Any support for adding this to pyfakefs? I'll gladly write some more docs if desired. Thanks for the feedback

[jmcgeheeiv]

"Any support for adding this to pyfakefs?"

You're so funny, @wesleykendall. Hell yeah there's support for that!

A paragraph or two in README.md would be appropriate for documentation.

This needs a test, which would require pytest, but on the other hand, we need to ensure that pyfakefs works without pytest. Ideas?

[wesleykendall]

@jmcgeheeiv awesome! Here's what I attempted to do in the most recent commits:

1. Updated tox and travis to run py.test on one pytest test file to ensure the fixture is available (had to add a "pip install ." beforehand for the entry point).
2. Removed the conftest.py file. I'm assuming this was just example code. It interfered with my pytest since it also defined the "fs" fixture.
3. Updated the README to have a small subsection about usage of the pytest plugin

Anything else that might be worth adding? I can update the wiki too.

Something worth noting - pytest has deprecated yield_fixture for using fixture, but using fixture will fail with <pytest3 right now. I don't know of an easy way to test out compatibility until pytest officially removes yield_fixture.

[mrbean-bremen]

You could check for the pytest version to decide which decorator to use. Something along the lines of:

from distutils.version import LooseVersion

is_pytest2 = LooseVersion(pytest.__version__) < LooseVersion('3')
pytest_fixture = pytest.yield_fixture if is_pytest2 else pytest.fixture

@pytest_fixture
def fs()
...

Edit: ok, you already fixed this in a nicer way while I was writing :)
Ignore the comment...

[wesleykendall]

@mrbean-bremen @jmcgeheeiv I just got around this issue with using addFinalizer 4deb644

[jmcgeheeiv]

@mrbean-bremen, you have been watching this PR more carefully than me, so please take care of the merge as you see fit. @wesleykendall, thanks a bunch for the contribution!

[jmcgeheeiv]

@megapctr, I think you will be interested in this new capability.

[mrbean-bremen]

@wesleykendall, thanks a lot!

[wesleykendall]

@mrbean-bremen @jmcgeheeiv Thanks! Any idea when this will be released?

[mrbean-bremen]

I certainly would plead for a new release here, as this change makes using pytest with pyfakefs much more convenient - though @jmcgeheeiv has to do the release work, and we just had a release...

[jmcgeheeiv]

I'll see what I can do this weekend.

[jmcgeheeiv]

@wesleykendall, @mrbean-bremen, @megapctr
pyfakefs version 3.1 released with pytest fixture.

[mrbean-bremen]

Thanks - that was fast!

[wesleykendall]

Thanks!