Merge lp:~gnuoy/charm-helpers/add-packacerevno-method into lp:charm-helpers

[Liam Young]

=== modified file 'charmhelpers/core/host.py'
--- charmhelpers/core/host.py	2014-02-26 15:53:02 +0000
+++ charmhelpers/core/host.py	2014-05-14 12:29:05 +0000
@@ -12,6 +12,7 @@
 import string
 import subprocess
 import hashlib
+import apt_pkg
 
 from collections import OrderedDict
 
@@ -295,3 +296,16 @@
     if 'link/ether' in words:
         hwaddr = words[words.index('link/ether') + 1]
     return hwaddr
+
+
+def cmp_pkgrevno(package, revno, pkgcache=None):
+    '''Compare supplied revno with the revno of the installed package
+       1 => Installed revno is greater than supplied arg
+       0 => Installed revno is the same as supplied arg
+      -1 => Installed revno is less than supplied arg
+    '''
+    if not pkgcache:
+        apt_pkg.init()
+        pkgcache = apt_pkg.Cache()
+    pkg = pkgcache[package]
+    return apt_pkg.version_compare(pkg.current_ver.ver_str, revno)
 
=== modified file 'tests/core/test_host.py'
--- tests/core/test_host.py	2013-11-29 11:24:48 +0000
+++ tests/core/test_host.py	2014-05-14 12:29:05 +0000
@@ -1,5 +1,6 @@
 from collections import OrderedDict
 import subprocess
+import apt_pkg
 
 from mock import patch, call
 from testtools import TestCase
@@ -690,3 +691,21 @@
         nic = "eth0"
         hwaddr = host.get_nic_hwaddr(nic)
         self.assertEqual(hwaddr, 'e4:11:5b:ab:a7:3c')
+
+    @patch.object(apt_pkg, 'Cache')
+    def test_cmp_pkgrevno_revnos(self, pkg_cache):
+        class MockPackage:
+            class MockPackageRevno:
+                def __init__(self, ver_str):
+                    self.ver_str = ver_str
+
+            def __init__(self, current_ver):
+                self.current_ver = self.MockPackageRevno(current_ver)
+
+        pkg_dict = {
+            'python': MockPackage('2.4')
+        }
+        pkg_cache.return_value = pkg_dict
+        self.assertEqual(host.cmp_pkgrevno('python', '2.3'), 1)
+        self.assertEqual(host.cmp_pkgrevno('python', '2.4'), 0)
+        self.assertEqual(host.cmp_pkgrevno('python', '2.5'), -1)