Index: Lib/test/test_argparse.py
===================================================================
--- Lib/test/test_argparse.py	(revision 83954)
+++ Lib/test/test_argparse.py	(working copy)
@@ -26,6 +26,13 @@
             print(obj2)
         super(TestCase, self).assertEqual(obj1, obj2)
 
+    def setUp(self):
+        # The tests assume that line wrapping occurs at 80 columns, but this
+        # behaviour can be overridden by setting the COLUMNS environment
+        # variable.  To ensure that this assumption is true, unset COLUMNS.
+        env = support.EnvironmentVarGuard()
+        del env["COLUMNS"]
+        self.addCleanup(env.revert)
 
 
 class TempDirMixin(object):
@@ -1715,6 +1722,7 @@
         return parser
 
     def setUp(self):
+        super().setUp()
         self.parser = self._get_parser()
         self.command_help_parser = self._get_parser(subparser_help=True)
 
@@ -1942,6 +1950,7 @@
         self.assertRaises(ArgumentParserError, *args, **kwargs)
 
     def setUp(self):
+        super().setUp()
         self.wxyz_parent = ErrorRaisingArgumentParser(add_help=False)
         self.wxyz_parent.add_argument('--w')
         x_group = self.wxyz_parent.add_argument_group('x')
Index: Lib/test/support.py
===================================================================
--- Lib/test/support.py	(revision 83954)
+++ Lib/test/support.py	(working copy)
@@ -692,6 +692,9 @@
         return self
 
     def __exit__(self, *ignore_exc):
+        self.revert()
+
+    def revert(self):
         for (k, v) in self._changed.items():
             if v is None:
                 if k in self._environ: