Index: Lib/test/test_file.py
===================================================================
--- Lib/test/test_file.py	(revision 71904)
+++ Lib/test/test_file.py	(working copy)
@@ -129,6 +129,16 @@
     def testReadWhenWriting(self):
         self.assertRaises(IOError, self.f.read)
 
+    def testWriteWhenReading(self):
+        self.f.close()
+        self.f = self.open(TESTFN, 'r')
+        self.assertRaises(IOError, self.f.write, "teststring")
+
+    def testWriteWhenReadingBinary(self):
+        self.f.close()
+        self.f = self.open(TESTFN, 'rb')
+        self.assertRaises(IOError, self.f.write, b"teststring")
+        
 class CAutoFileTests(AutoFileTests):
     open = io.open