added test for is_allowed_string returning false, edited test for is_allowed_string returning true by adding a division

src/test/py/test_read_math_function.py

@@ -12,7 +12,9 @@ class read_function(unittest.TestCase):
     def test_constant_isstring_false(self):
         self.assertEqual(is_string(42), False)
     def test_constant_isallowed_string_true(self):
-        self.assertEqual(is_allowed_string("c", "42^(2)+1-3*4"), True)
+        self.assertEqual(is_allowed_string("c", "42^(2)+1-3*4/3"), True)
+    def test_constant_isallowed_string_false(self):
+        self.assertEqual(is_allowed_string("c", "42^(2)+1-3*4/3x"), False)
 
 if __name__ == '__main__':
     unittest.main()