bpo-40648: Test modes that file can get with chmod() on Windows (GH-20130)

Order of tests matter second part makes testing file writable and
possible to remove again.

Author: scrool

Lib/test/test_stat.py

@@ -148,12 +148,19 @@ def test_mode(self):
             self.assertEqual(modestr, '-r--r--r--')
             self.assertEqual(self.statmod.S_IMODE(st_mode), 0o444)
         else:
+            os.chmod(TESTFN, 0o500)
+            st_mode, modestr = self.get_mode()
+            self.assertEqual(modestr[:3], '-r-')
+            self.assertS_IS("REG", st_mode)
+            self.assertEqual(self.statmod.S_IMODE(st_mode), 0o444)
+
             os.chmod(TESTFN, 0o700)
             st_mode, modestr = self.get_mode()
             self.assertEqual(modestr[:3], '-rw')
             self.assertS_IS("REG", st_mode)
             self.assertEqual(self.statmod.S_IFMT(st_mode),
                              self.statmod.S_IFREG)
+            self.assertEqual(self.statmod.S_IMODE(st_mode), 0o666)
 
     @os_helper.skip_unless_working_chmod
     def test_directory(self):

Misc/NEWS.d/next/Tests/2020-05-16-18-00-21.bpo-40648.p2uPqy.rst

@@ -0,0 +1 @@
+Test modes that file can get with chmod() on Windows.