Provide more specific error when namespace is missing

Previously if a non-existent namespace was specified, we just got
a generic KeyError from stevedore that didn't say a whole lot about
what went wrong. You pretty much had to go read the code to figure
out what happened.

This change adds an explicit check for a missing namespace and raises
a KeyError with a more specific error message that explains what is
wrong.

Change-Id: Ia56d4655d70cee78661567188a977f67b7c3ee78
Closes-Bug: 1817953

2 files changed, 20 insertions, 0 deletions

diff --git a/oslo_policy/generator.py b/oslo_policy/generator.py
index c6ecd5b..1ea768e 100644
--- a/oslo_policy/generator.py
+++ b/oslo_policy/generator.py
@@ -84,6 +84,8 @@ def _get_enforcer(namespace):
         names=[namespace],
         on_load_failure_callback=on_load_failure_callback,
         invoke_on_load=True)
+    if namespace not in mgr:
+        raise KeyError('Namespace "%s" not found.' % namespace)
     enforcer = mgr[namespace].obj
 
     return enforcer
diff --git a/oslo_policy/tests/test_generator.py b/oslo_policy/tests/test_generator.py
index 98355ff..ab0940a 100644
--- a/oslo_policy/tests/test_generator.py
+++ b/oslo_policy/tests/test_generator.py
@@ -675,3 +675,21 @@ class UpgradePolicyTestCase(base.PolicyBaseTestCase):
                 expected = '''new_policy_name: rule:admin
 '''
                 self.assertEqual(expected, stdout.getvalue())
+
+
+@mock.patch('stevedore.named.NamedExtensionManager')
+class GetEnforcerTestCase(base.PolicyBaseTestCase):
+    def test_get_enforcer(self, mock_manager):
+        mock_instance = mock.MagicMock()
+        mock_instance.__contains__.return_value = True
+        mock_manager.return_value = mock_instance
+        mock_item = mock.Mock()
+        mock_item.obj = 'test'
+        mock_instance.__getitem__.return_value = mock_item
+        self.assertEqual('test', generator._get_enforcer('foo'))
+
+    def test_get_enforcer_missing(self, mock_manager):
+        mock_instance = mock.MagicMock()
+        mock_instance.__contains__.return_value = False
+        mock_manager.return_value = mock_instance
+        self.assertRaises(KeyError, generator._get_enforcer, 'nonexistent')