backport r67325: make FileIO.mode always contain 'b'
diff --git a/Lib/test/test_fileio.py b/Lib/test/test_fileio.py
index cbc7165..c978779 100644
--- a/Lib/test/test_fileio.py
+++ b/Lib/test/test_fileio.py
@@ -50,7 +50,7 @@
         # verify expected attributes exist
         f = self.f
 
-        self.assertEquals(f.mode, "w")
+        self.assertEquals(f.mode, "wb")
         self.assertEquals(f.closed, False)
 
         # verify the attributes are readonly
@@ -160,7 +160,7 @@
 
     def testModeStrings(self):
         # check invalid mode strings
-        for mode in ("", "aU", "wU+", "rb", "rt"):
+        for mode in ("", "aU", "wU+", "rw", "rt"):
             try:
                 f = _fileio._FileIO(TESTFN, mode)
             except ValueError: