plugin_ep.problem unittests

and some misc style things

letsencrypt/cli.py

@@ -351,8 +351,8 @@ def diagnose_configurator_problem(cfg_type, requested, plugins):
             msg = "The requested {0} plugin does not appear to be installed".format(requested)
         else:
             msg = ("The {0} plugin is not working; there may be problems with "
-                   "your existing configuration.\nThe error was: {1}"
-                   .format(requested, `plugins[requested].problem`))
+                   "your existing configuration.\nThe error was: {1!r}"
+                   .format(requested, plugins[requested].problem))
     elif cfg_type == "installer":
         if os.path.exists("/etc/debian_version"):
             # Debian... installers are at least possible

letsencrypt/plugins/disco.py

@@ -125,6 +125,7 @@ class PluginEntryPoint(object):
         """Return the Exception raised during plugin setup, or None if all is well"""
         if isinstance(self._prepared, Exception):
             return self._prepared
+        return None
 
     @property
     def available(self):

letsencrypt/plugins/disco_test.py

@@ -68,6 +68,7 @@ class PluginEntryPointTest(unittest.TestCase):
         self.assertFalse(self.plugin_ep.prepared)
         self.assertFalse(self.plugin_ep.misconfigured)
         self.assertFalse(self.plugin_ep.available)
+        self.assertTrue(self.plugin_ep.problem is None)
         self.assertTrue(self.plugin_ep.entry_point is EP_SA)
         self.assertEqual("sa", self.plugin_ep.name)
 
@@ -131,6 +132,8 @@ class PluginEntryPointTest(unittest.TestCase):
                                    errors.MisconfigurationError))
         self.assertTrue(self.plugin_ep.prepared)
         self.assertTrue(self.plugin_ep.misconfigured)
+        self.assertTrue(isinstance(self.plugin_ep.problem,
+                                   errors.MisconfigurationError))
         self.assertTrue(self.plugin_ep.available)
 
     def test_prepare_no_installation(self):