bpo-40275: Use new test.support helper submodules in tests (GH-21315)

diff --git a/Lib/test/test_file.py b/Lib/test/test_file.py
index cd642e7..1497675 100644
--- a/Lib/test/test_file.py
+++ b/Lib/test/test_file.py
@@ -7,8 +7,9 @@
 import io
 import _pyio as pyio
 
-from test.support import TESTFN
-from test import support
+from test.support.os_helper import TESTFN
+from test.support import os_helper
+from test.support import warnings_helper
 from collections import UserList
 
 class AutoFileTests:
@@ -20,7 +21,7 @@
     def tearDown(self):
         if self.f:
             self.f.close()
-        support.unlink(TESTFN)
+        os_helper.unlink(TESTFN)
 
     def testWeakRefs(self):
         # verify weak references
@@ -139,7 +140,7 @@
 class OtherFileTests:
 
     def tearDown(self):
-        support.unlink(TESTFN)
+        os_helper.unlink(TESTFN)
 
     def testModeStrings(self):
         # check invalid mode strings
@@ -187,7 +188,7 @@
         # make sure that explicitly setting the buffer size doesn't cause
         # misbehaviour especially with repeated close() calls
         for s in (-1, 0, 512):
-            with support.check_no_warnings(self,
+            with warnings_helper.check_no_warnings(self,
                                            message='line buffering',
                                            category=RuntimeWarning):
                 self._checkBufferSize(s)