From fed07711c1a1870501fde6043adaef1350fb3c49 Mon Sep 17 00:00:00 2001
From: Auke Willem Oosterhoff <awoosterhoff@gmail.com>
Date: Wed, 27 Jan 2016 21:58:04 +0100
Subject: [PATCH] #24 Test redundancy_check module.

---
 tests/unit/client/serial/__init__.py          |  0
 .../client/serial/test_redundancy_check.py    | 23 +++++++++++++++++++
 umodbus/client/serial/redundancy_check.py     |  6 ++---
 3 files changed, 26 insertions(+), 3 deletions(-)
 create mode 100644 tests/unit/client/serial/__init__.py
 create mode 100644 tests/unit/client/serial/test_redundancy_check.py

diff --git a/tests/unit/client/serial/__init__.py b/tests/unit/client/serial/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/unit/client/serial/test_redundancy_check.py b/tests/unit/client/serial/test_redundancy_check.py
new file mode 100644
index 0000000..b22d632
--- /dev/null
+++ b/tests/unit/client/serial/test_redundancy_check.py
@@ -0,0 +1,23 @@
+import struct
+import pytest
+
+from umodbus.client.serial.redundancy_check import get_crc, validate_crc
+
+
+def test_get_crc():
+    """ Test if correct CRC is calculated. """
+    # Values are equal to those used in example in MODBUS over serial line
+    # specification and implementation guide V1.02, chapter 6.2.2.
+    assert struct.unpack('<H', get_crc(b'\x02\x07')) ==\
+        struct.unpack('<H', b'\x41\x12')
+
+
+def test_validate_valid_crc():
+    """" Method should not raise assertion error. """
+    validate_crc(b'\x02\x07', b'\x41\x12')
+
+
+def test_validate_invalid_crc():
+    """" Method should raise assertion error. """
+    with pytest.raises(AssertionError):
+        validate_crc(b'\x02\x07', b'\x41\x11')
diff --git a/umodbus/client/serial/redundancy_check.py b/umodbus/client/serial/redundancy_check.py
index 3380e2a..de9c794 100644
--- a/umodbus/client/serial/redundancy_check.py
+++ b/umodbus/client/serial/redundancy_check.py
@@ -34,8 +34,7 @@ def generate_look_up_table():
 def get_crc(msg):
     """ Return CRC of 2 byte for message.
 
-        >>> assert get_crc('<H', b'\x02\x07') ==\
-                struct.unpack('<H', b'\x41\x12')
+        >>> assert get_crc(b'\x02\x07') == struct.unpack('<H', b'\x41\x12')
 
     :param msg: A byte array.
     :return: Byte array of 2 bytes.
@@ -43,8 +42,9 @@ def get_crc(msg):
     register = 0xFFFF
 
     for byte_ in msg:
+        val = struct.unpack('<B', byte_)[0]
         register = \
-            (register >> 8) ^ look_up_table[(register ^ byte_) & 0xFF]
+            (register >> 8) ^ look_up_table[(register ^ val) & 0xFF]
 
     # CRC is little-endian!
     return struct.pack('<H', register)