Avoid replacing existing modules and sys.path in import tests

Lib/test/test_imp.py

@@ -43,14 +43,17 @@ class ReloadTests(unittest.TestCase):
     reload()."""
 
     def test_source(self):
+        with test_support.CleanImport('os'):
             import os
             imp.reload(os)
 
     def test_extension(self):
+        with test_support.CleanImport('time'):
             import time
             imp.reload(time)
 
     def test_builtin(self):
+        with test_support.CleanImport('marshal'):
             import marshal
             imp.reload(marshal)
 

Lib/test/test_import.py

@@ -8,7 +8,7 @@ import py_compile
 import warnings
 import marshal
 from test.test_support import (unlink, TESTFN, unload, run_unittest,
-    check_warnings, TestFailed)
+    check_warnings, TestFailed, CleanImport)
 
 
 def remove_files(name):
@@ -122,6 +122,7 @@ class ImportTest(unittest.TestCase):
     def testImpModule(self):
         # Verify that the imp module can correctly load and find .py files
         import imp
+        with CleanImport("os"):
             x = imp.find_module("os")
             os = imp.load_module("os", *x)
 
@@ -361,7 +362,7 @@ class PathsTests(unittest.TestCase):
 
     def tearDown(self):
         shutil.rmtree(self.path)
-        sys.path = self.syspath
+        sys.path[:] = self.syspath
 
     # http://bugs.python.org/issue1293
     def test_trailing_slash(self):