diff --git a/nova/exception.py b/nova/exception.py
index c908e5d85f49..42c50ea8e28f 100644
--- a/nova/exception.py
+++ b/nova/exception.py
@@ -86,17 +86,21 @@ class NovaException(Exception):
                 message = self.msg_fmt % kwargs
 
             except Exception:
-                # kwargs doesn't match a variable in the message
-                # log the issue and the kwargs
-                LOG.exception(_LE('Exception in string format operation'))
-                for name, value in kwargs.items():
-                    LOG.error("%s: %s" % (name, value))  # noqa
-
+                # NOTE(melwitt): This is done in a separate method so it can be
+                # monkey-patched during testing to make it a hard failure.
+                self._log_exception()
                 message = self.msg_fmt
 
         self.message = message
         super(NovaException, self).__init__(message)
 
+    def _log_exception(self):
+        # kwargs doesn't match a variable in the message
+        # log the issue and the kwargs
+        LOG.exception(_LE('Exception in string format operation'))
+        for name, value in self.kwargs.items():
+            LOG.error("%s: %s" % (name, value))  # noqa
+
     def format_message(self):
         # NOTE(mrodden): use the first argument to the python Exception object
         # which should be our full NovaException message, (see __init__)
diff --git a/nova/test.py b/nova/test.py
index d6e4d59a62f0..be20f539820a 100644
--- a/nova/test.py
+++ b/nova/test.py
@@ -31,6 +31,7 @@ import datetime
 import inspect
 import os
 import pprint
+import sys
 
 import fixtures
 import mock
@@ -49,6 +50,7 @@ import testtools
 
 from nova import context
 from nova import db
+from nova import exception
 from nova.network import manager as network_manager
 from nova.network.security_group import openstack_driver
 from nova import objects
@@ -169,6 +171,26 @@ def _patch_mock_to_raise_for_invalid_assert_calls():
 _patch_mock_to_raise_for_invalid_assert_calls()
 
 
+class NovaExceptionReraiseFormatError(object):
+    real_log_exception = exception.NovaException._log_exception
+
+    @classmethod
+    def patch(cls):
+        exception.NovaException._log_exception = cls._wrap_log_exception
+
+    @staticmethod
+    def _wrap_log_exception(self):
+        exc_info = sys.exc_info()
+        NovaExceptionReraiseFormatError.real_log_exception(self)
+        six.reraise(*exc_info)
+
+
+# NOTE(melwitt) This needs to be done at import time in order to also catch
+# NovaException format errors that are in mock decorators. In these cases, the
+# errors will be raised during test listing, before tests actually run.
+NovaExceptionReraiseFormatError.patch()
+
+
 class TestCase(testtools.TestCase):
     """Test case base class for all unit tests.
 
diff --git a/nova/tests/unit/test_exception.py b/nova/tests/unit/test_exception.py
index 816bf06b01f3..0c698e26c265 100644
--- a/nova/tests/unit/test_exception.py
+++ b/nova/tests/unit/test_exception.py
@@ -16,6 +16,7 @@
 
 import inspect
 
+import fixtures
 import mock
 import six
 from webob.util import status_reasons
@@ -211,6 +212,13 @@ class NovaExceptionTestCase(test.NoDBTestCase):
         self.assertEqual("some message", exc.format_message())
 
     def test_format_message_remote_error(self):
+        # NOTE(melwitt): This test checks that errors are formatted as expected
+        # in a real environment where format errors are caught and not
+        # reraised, so we patch in the real implementation.
+        self.useFixture(fixtures.MonkeyPatch(
+            'nova.exception.NovaException._log_exception',
+            test.NovaExceptionReraiseFormatError.real_log_exception))
+
         class FakeNovaException_Remote(exception.NovaException):
             msg_fmt = "some message %(somearg)s"
 
diff --git a/nova/tests/unit/test_test.py b/nova/tests/unit/test_test.py
index 1991dfe89322..70030af9f58f 100644
--- a/nova/tests/unit/test_test.py
+++ b/nova/tests/unit/test_test.py
@@ -21,6 +21,7 @@ import oslo_messaging as messaging
 import six
 
 import nova.conf
+from nova import exception
 from nova import rpc
 from nova import test
 from nova.tests import fixtures
@@ -283,3 +284,20 @@ class ContainKeyValueTestCase(test.NoDBTestCase):
         # Raise KeyError
         self.assertNotEqual(matcher, {1: 2, '3': 4, 5: '6'})
         self.assertNotEqual(matcher, {'bar': 'foo'})
+
+
+class NovaExceptionReraiseFormatErrorTestCase(test.NoDBTestCase):
+    """Test that format errors are reraised in tests."""
+    def test_format_error_in_nova_exception(self):
+        class FakeImageException(exception.NovaException):
+            msg_fmt = 'Image %(image_id)s has wrong type %(type)s.'
+        # wrong kwarg
+        ex = self.assertRaises(KeyError, FakeImageException,
+                               bogus='wrongkwarg')
+        self.assertIn('image_id', six.text_type(ex))
+        # no kwarg
+        ex = self.assertRaises(KeyError, FakeImageException)
+        self.assertIn('image_id', six.text_type(ex))
+        # not enough kwargs
+        ex = self.assertRaises(KeyError, FakeImageException, image_id='image')
+        self.assertIn('type', six.text_type(ex))