use io.SEEK_* constants instead of os.SEEK_* where an IO stream is seeked, leaving the os.SEEK_* constants only for os.lseek, as documented
diff --git a/Lib/test/test_fileio.py b/Lib/test/test_fileio.py
index 103365d..75db82c 100644
--- a/Lib/test/test_fileio.py
+++ b/Lib/test/test_fileio.py
@@ -2,6 +2,7 @@
 
 import sys
 import os
+import io
 import errno
 import unittest
 from array import array
@@ -334,10 +335,10 @@
         self.assertEqual(f.tell(), 10)
         f.truncate(5)
         self.assertEqual(f.tell(), 10)
-        self.assertEqual(f.seek(0, os.SEEK_END), 5)
+        self.assertEqual(f.seek(0, io.SEEK_END), 5)
         f.truncate(15)
         self.assertEqual(f.tell(), 5)
-        self.assertEqual(f.seek(0, os.SEEK_END), 15)
+        self.assertEqual(f.seek(0, io.SEEK_END), 15)
         f.close()
 
     def testTruncateOnWindows(self):