Use py.test to launch pytest, rather than python -m test, preventing the empty...

Use py.test to launch pytest, rather than python -m test, preventing the empty path from being added to sys.path per pytest-dev/pytest#2104. Fixes #852. Also use 'usedevelop' as the setuptools.tests.fixtures aren't available in a standard install.

conftest.py

-import os
-
-
 pytest_plugins = 'setuptools.tests.fixtures'
 
 
@@ -9,17 +6,3 @@ def pytest_addoption(parser):
         "--package_name", action="append", default=[],
         help="list of package_name to pass to test functions",
     )
-
-
-def pytest_configure():
-    _issue_852_workaround()
-
-
-def _issue_852_workaround():
-    """
-    Patch 'setuptools.__file__' with an absolute path
-    for forward compatibility with Python 3.
-    Workaround for https://github.com/pypa/setuptools/issues/852
-    """
-    setuptools = __import__('setuptools')
-    setuptools.__file__ = os.path.abspath(setuptools.__file__)

tox.ini

 [testenv]
 deps=-rtests/requirements.txt
 passenv=APPDATA USERPROFILE HOMEDRIVE HOMEPATH windir APPVEYOR
-commands=python -m pytest {posargs:-rsx}
+commands=py.test {posargs:-rsx}
+usedevelop=True