# HG changeset patch
# User Brian Neal <bgneal@gmail.com>
# Date 1338086583 18000
# Node ID 9ca7c7a93fc270ec3f211c4d33176e54fc9e21ef
# Parent  f6edbbd35b9277fc0fad20375a061b6703c0dd46
Added a test for "double stepping".

diff -r f6edbbd35b92 -r 9ca7c7a93fc2 enigma/machine.py
--- a/enigma/machine.py	Sat May 26 20:05:07 2012 -0500
+++ b/enigma/machine.py	Sat May 26 21:43:03 2012 -0500
@@ -57,6 +57,13 @@
         for i, r in enumerate(range(start, self.rotor_count)):
             self.rotors[r].set_display(val[i])
 
+    def get_display(self):
+        """Returns the operator display as a string."""
+
+        return "{}{}{}".format(self.rotors[-3].get_display(),
+                               self.rotors[-2].get_display(),
+                               self.rotors[-1].get_display())
+
     def key_press(self, key):
         """Simulate a front panel key press. 
 
diff -r f6edbbd35b92 -r 9ca7c7a93fc2 enigma/tests/test_enigma.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/enigma/tests/test_enigma.py	Sat May 26 21:43:03 2012 -0500
@@ -0,0 +1,36 @@
+# Copyright (C) 2012 by Brian Neal.
+# This file is part of Py-Enigma, the Enigma Machine simulation.
+# Py-Enigma is released under the MIT License (see License.txt).
+
+"""Tests for the EnigmaMachine class."""
+
+import unittest
+
+from ..rotors.factory import create_rotor, create_reflector
+from ..machine import EnigmaMachine
+
+
+class EnigmaMachineTestCase(unittest.TestCase):
+
+    def test_double_stepping(self):
+        """Ensure the rotors step realistically by testing for a "double-step"
+        case.
+        
+        """
+        # This example taken from 
+        # http://users.telenet.be/d.rijmenants/en/enigmatech.htm
+        # in the section on "The Stepping Mechanism."
+        rotors = []
+        rotors.append(create_rotor("III"))
+        rotors.append(create_rotor("II"))
+        rotors.append(create_rotor("I"))
+
+        m = EnigmaMachine(rotors, create_reflector('B'))
+
+        m.set_display('KDO')
+
+        truth_data = ['KDP', 'KDQ', 'KER', 'LFS', 'LFT', 'LFU']
+        for expected in truth_data:
+            m.key_press('A')
+            self.assertEqual(m.get_display(), expected)
+