utils: fix Severity(None) condition

This patch fixes Severity.__init__() when it is not given an argument to
raise an AppArmor exception rather than returning a Severity object in
an incompletely initialized state. It also adjusts a test case covering
this situation.

Signed-off-by: Steve Beattie <steve@nxnw.org>
Acked-by: Christian Boltz <apparmor@cboltz.de>

utils/apparmor/severity.py

@@ -29,7 +29,7 @@ class Severity(object):
         # For variable expansions for the profile
         self.severity['VARIABLES'] = dict()
         if not dbname:
-            return None
+            raise AppArmorException("No severity db file given")
 
         with open_file_read(dbname) as database:  # open(dbname, 'r')
             for lineno, line in enumerate(database, start=1):

utils/test/severity_test.py

@@ -206,8 +206,8 @@ class SeverityDBTest(unittest.TestCase):
         self.assertRaises(IOError, severity.Severity, 'severity.db.does.not.exist')
 
     def test_no_arg_to_severity(self):
-        sev_db = severity.Severity()
-        self.assertIsNone(sev_db, 'expected None, got %s' % (sev_db))
+        with self.assertRaises(AppArmorException):
+            severity.Severity()
 
 if __name__ == "__main__":
     unittest.main(verbosity=2)