Add an additional test: BZ2File write methods should raise IOError

when file is read-only.

Lib/test/test_bz2.py

@@ -172,6 +172,15 @@ class BZ2FileTest(BaseTest):
         self.assertEqual(self.decompress(f.read()), self.TEXT)
         f.close()
 
+    def testWriteMethodsOnReadOnlyFile(self):
+        bz2f = BZ2File(self.filename, "w")
+        bz2f.write("abc")
+        bz2f.close()
+
+        bz2f = BZ2File(self.filename, "r")
+        self.assertRaises(IOError, bz2f.write, "a")
+        self.assertRaises(IOError, bz2f.writelines, ["a"])
+
     def testSeekForward(self):
         # "Test BZ2File.seek(150, 0)"
         self.createTempFile()