Refactor test setup for temporary directories

setup.py

@@ -13,7 +13,8 @@ with open('README.md') as f:
 
 def get_version(package):
     """Return package version as listed in `__version__` in `init.py`."""
-    init_py = open(os.path.join(package, '__init__.py')).read()
+    with open(os.path.join(package, '__init__.py')) as f:
+        init_py = f.read()
     return re.search("__version__ = ['\"]([^'\"]+)['\"]", init_py).group(1)