Fix exception on Python3 in _link_read_permaddress

Bytestrings need to be decoded. Just use UTF-8 here, since everyone
should be using it. Also add a test case to catch this. The exception
was:
TypeError: cannot use a string pattern on a bytes-like object

library/network_connections.py

@@ -74,7 +74,8 @@ class Util:
             ev = os.environ.copy()
             ev['LANG'] = lang if lang is not None else 'C'
             p = subprocess.Popen(argv, stdout=subprocess.PIPE, stderr=DEVNULL, env=ev)
-            out = p.communicate()[0]
+            # FIXME: Can we assume this to always be UTF-8?
+            out = p.communicate()[0].decode("UTF-8")
             if p.returncode != 0:
                 raise MyError('failure calling %s: exit with %s' % (argv, p.returncode))
         return out

tests/helpers/ethtool

@@ -0,0 +1,6 @@
+#! /bin/bash
+
+if [ "${1}" == "-P" ] && [ "${2}" != "" ]
+then
+    echo "Permanent address: 23:00:00:00:00:00"
+fi

tests/test_network_connections.py

@@ -7,10 +7,12 @@ import unittest
 import socket
 import itertools
 
-sys.path.insert(1, os.path.join(os.path.dirname(os.path.abspath(__file__)),
-                                "..", "library"))
+TESTS_BASEDIR = os.path.dirname(os.path.abspath(__file__))
+sys.path.insert(1, os.path.join(TESTS_BASEDIR, "..", "library"))
 
 import network_connections as n
+from network_connections import SysUtil
+
 
 try:
     my_test_skipIf = unittest.skipIf
@@ -1873,5 +1875,15 @@ class TestNM(unittest.TestCase):
         self.assertIs(s, s2)
         self.assertTrue(GObject.type_is_a(s, NM.SettingWired))
 
+
+class TestSysUtils(unittest.TestCase):
+    def test_link_read_permaddress(self):
+        # Manipulate PATH to use ethtool mock script to avoid hard dependency on
+        # ethtool
+        os.environ["PATH"] = TESTS_BASEDIR + "/helpers:" + os.environ["PATH"]
+        self.assertEqual(SysUtil._link_read_permaddress("lo"),
+                         "23:00:00:00:00:00")
+
+
 if __name__ == '__main__':
     unittest.main()

tests/tests_unit.yml

@@ -11,6 +11,16 @@
         src: test_network_connections.py
         dest: /tmp/test-unit-1/
 
+    - file:
+        state: directory
+        dest: /tmp/test-unit-1/helpers
+
+    - copy:
+        src: "{{ item }}"
+        dest: /tmp/test-unit-1/helpers
+        mode: 0755
+      with_fileglob:
+        - helpers/*
 
     - package:
         name: python2