Implement #7944. Use `with` throughout the test suite.

Lib/test/test_old_mailbox.py

@@ -48,18 +48,16 @@ class MaildirTestCase(unittest.TestCase):
         filename = os.extsep.join((str(t), str(pid), "myhostname", "mydomain"))
         tmpname = os.path.join(self._dir, "tmp", filename)
         newname = os.path.join(self._dir, dir, filename)
-        fp = open(tmpname, "w")
+        with open(tmpname, "w") as fp:
             self._msgfiles.append(tmpname)
             if mbox:
                 fp.write(FROM_)
             fp.write(DUMMY_MESSAGE)
-        fp.close()
         if hasattr(os, "link"):
             os.link(tmpname, newname)
         else:
-            fp = open(newname, "w")
+            with open(newname, "w") as fp:
                 fp.write(DUMMY_MESSAGE)
-            fp.close()
         self._msgfiles.append(newname)
         return tmpname
 
@@ -102,7 +100,8 @@ class MaildirTestCase(unittest.TestCase):
         import email.parser
         fname = self.createMessage("cur", True)
         n = 0
-        for msg in mailbox.PortableUnixMailbox(open(fname),
+        with open(fname) as f:
+            for msg in mailbox.PortableUnixMailbox(f,
                                                email.parser.Parser().parse):
                 n += 1
                 self.assertEqual(msg["subject"], "Simple Test")
@@ -119,7 +118,7 @@ class MboxTestCase(unittest.TestCase):
 
     def test_from_regex (self):
         # Testing new regex from bug #1633678
-        f = open(self._path, 'w')
+        with open(self._path, 'w') as f:
             f.write("""From fred@example.com Mon May 31 13:24:50 2004 +0200
 Subject: message 1
 
@@ -137,8 +136,8 @@ Subject: message 4
 
 body4
 """)
-        f.close()
-        box = mailbox.UnixMailbox(open(self._path, 'r'))
+        with open(self._path, 'r') as f:
+            box = mailbox.UnixMailbox(f)
             self.assertTrue(len(list(iter(box))) == 4)