Refactoring and tests for getting the lockdown form

Streamlines the get_lockdown_form method a bit and adds tests to check it for
properly returning exceptions in case of a form which couldn't be loaded.

lockdown/middleware.py

@@ -17,20 +17,22 @@ def compile_url_exceptions(url_exceptions):
 
 
 def get_lockdown_form(form_path):
-    form_path = settings.FORM
-    if not form_path or '.' not in form_path:
-        raise ImproperlyConfigured('The form module path was not provided.')
-    last_dot = form_path.rfind('.')
-    module, attr = form_path[:last_dot], form_path[last_dot + 1:]
+    if not form_path:
+        raise ImproperlyConfigured('No LOCKDOWN_FORM specified.')
+    form_path_list = form_path.split(".")
+    module = ".".join(form_path_list[:-1])
+    attr = form_path_list[-1]
     try:
         mod = import_module(module)
     except (ImportError, ValueError) as exc:
-        raise ImproperlyConfigured('Error importing LOCKDOWN_FORM %s: "%s"'
-                                   % (form_path, exc))
+        raise ImproperlyConfigured('Module configured in LOCKDOWN_FORM (%s) to'
+                                   ' contain the form class couldn\'t be '
+                                   'found.' % module)
     try:
         form = getattr(mod, attr)
     except AttributeError:
-        raise ImproperlyConfigured('Module "%s" does not define a "%s" form.'
+        raise ImproperlyConfigured('The module configured in LOCKDOWN_FORM '
+                                   ' (%s) doesn\'t define a "%s" form.'
                                    % (module, attr))
     return form
 

lockdown/tests/tests.py

@@ -1,10 +1,11 @@
 import datetime
 import os
 
-from django.test import TestCase
 from django.conf import settings as django_settings
+from django.core.exceptions import ImproperlyConfigured
+from django.test import TestCase
 
-from lockdown import settings, middleware
+from lockdown import middleware, settings
 from lockdown.forms import AuthForm
 
 __all__ = ['DecoratorTests', 'MiddlewareTests']
@@ -99,6 +100,22 @@ def test_custom_form(self):
             middleware._default_form = middleware.get_lockdown_form(
                 settings.FORM)
 
+    def test_invalid_custom_form(self):
+        """Test that pointing to an invalid form properly produces an error"""
+
+        # no form configured at all
+        self.assertRaises(ImproperlyConfigured,
+                          middleware.get_lockdown_form, None)
+        # invalid module name in the configured form
+        self.assertRaises(ImproperlyConfigured,
+                          middleware.get_lockdown_form, 'invalidform')
+        # not existing module for form
+        self.assertRaises(ImproperlyConfigured,
+                          middleware.get_lockdown_form, 'invalid.form')
+        # existing module, but no form with that name in the module
+        self.assertRaises(ImproperlyConfigured,
+                          middleware.get_lockdown_form, 'lockdown.forms.foo')
+
     def test_locked_until(self):
         _old_until_date = settings.UNTIL_DATE
         yesterday = datetime.datetime.now() - datetime.timedelta(days=1)