Issue #22854: Merge Windows pipe skipping from 3.5

Lib/test/test_io.py

@@ -424,13 +424,6 @@ class IOTest(unittest.TestCase):
                 self.assertEqual(obj.readable(), readable)
                 writable = "w" in abilities
                 self.assertEqual(obj.writable(), writable)
-                seekable = "s" in abilities
-
-                # Detection of pipes being non-seekable does not seem to work
-                # on Windows
-                if not sys.platform.startswith("win") or test not in (
-                        pipe_reader, pipe_writer):
-                    self.assertEqual(obj.seekable(), seekable)
 
                 if isinstance(obj, self.TextIOBase):
                     data = "3"
@@ -456,6 +449,13 @@ class IOTest(unittest.TestCase):
                 else:
                     self.assertRaises(OSError, obj.write, data)
 
+                if sys.platform.startswith("win") or test in (
+                        pipe_reader, pipe_writer):
+                    # Pipes seem to appear as seekable on Windows
+                    continue
+                seekable = "s" in abilities
+                self.assertEqual(obj.seekable(), seekable)
+
                 if seekable:
                     obj.tell()
                     obj.seek(0)