Typo fix

tests/tests_rpn_eval.py

@@ -117,7 +117,7 @@ class TestRpnEval(unittest.TestCase):
         self.assertEqual(res, 0)
 
 
-    def test_airthm_extended(self):
+    def test_arithm_extended(self):
         """ Extended arithmetic tests """
         exprs = (
             ('A0 A1 +', '{0} + {1}', 2),