posix.fdopen does not exists any more; and os.fdopen exists on all platforms.

Move tests from test_posix to test_os.

Lib/test/test_os.py

@@ -134,6 +134,16 @@ class TemporaryFileTests(unittest.TestCase):
         else:
             self.check_tempfile(name)
 
+    def fdopen_helper(self, *args):
+        fd = os.open(support.TESTFN, os.O_RDONLY)
+        fp2 = os.fdopen(fd, *args)
+        fp2.close()
+
+    def test_fdopen(self):
+        self.fdopen_helper()
+        self.fdopen_helper('r')
+        self.fdopen_helper('r', 100)
+
 # Test attributes on return values from os.*stat* family.
 class StatAttributeTests(unittest.TestCase):
     def setUp(self):

Lib/test/test_posix.py

@@ -89,17 +89,6 @@ class PosixTester(unittest.TestCase):
                 fp1.close()
                 fp2.close()
 
-    def fdopen_helper(self, *args):
-        fd = os.open(support.TESTFN, os.O_RDONLY)
-        fp2 = posix.fdopen(fd, *args)
-        fp2.close()
-
-    def test_fdopen(self):
-        if hasattr(posix, 'fdopen'):
-            self.fdopen_helper()
-            self.fdopen_helper('r')
-            self.fdopen_helper('r', 100)
-
     def test_osexlock(self):
         if hasattr(posix, "O_EXLOCK"):
             fd = os.open(support.TESTFN,