use sysconfig from pep425tags and use mock's patch context mgr

Author: qwcode

tests/unit/test_wheel.py

@@ -150,33 +150,27 @@ def test_unpack_wheel_no_flatten(self):
         finally:
             rmtree(tmpdir)
             pass
-        
+
     def test_purelib_platlib(self):
         """
         Test the "wheel is purelib/platlib" code.
         """
         packages =  [("pure_wheel", "data/packages/pure_wheel-1.7", True),
-                     ("plat_wheel", "data/packages/plat_wheel-1.7", False)]        
+                     ("plat_wheel", "data/packages/plat_wheel-1.7", False)]
         for name, path, expected in packages:
             assert wheel.root_is_purelib(name, path) == expected
 
 class TestPEP425Tags(object):
-    
+
     def test_broken_sysconfig(self):
         """
         Test that pep425tags still works when sysconfig is broken.
         Can be a problem on Python 2.7
         Issue #1074.
         """
-        import sysconfig
         import pip.pep425tags
         def raises_ioerror(var):
             raise IOError("I have the wrong path!")
-
-        original = sysconfig.get_config_var
-        sysconfig.get_config_var = raises_ioerror
-        try:
+        with patch('pip.pep425tags.sysconfig.get_config_var', raises_ioerror):
             assert len(pip.pep425tags.get_supported())
-        finally:
-            sysconfig.get_config_var = original