diff --git a/swh/web/ui/tests/test_controller.py b/swh/web/ui/tests/test_controller.py
index 0ad3fd3b..dc9d9088 100644
--- a/swh/web/ui/tests/test_controller.py
+++ b/swh/web/ui/tests/test_controller.py
@@ -1,150 +1,165 @@
 # Copyright (C) 2015  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU Affero General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 import unittest
 import json
 
 from nose.tools import istest
 from unittest.mock import patch
 
 from swh.web.ui.tests import test_app
 
 
 class ApiTestCase(unittest.TestCase):
 
     @classmethod
     def setUpClass(cls):
         cls.app, _, _ = test_app.init_app()
 
     @istest
     def info(self):
         # when
         rv = self.app.get('/about')
 
         self.assertEquals(rv.status_code, 200)
         self.assertIn(b'About', rv.data)
 
     # @istest
     def search_1(self):
         # when
         rv = self.app.get('/search')
 
         self.assertEquals(rv.status_code, 200)  # check this api
         self.assertRegexpMatches(rv.data, b'name=q value=>')
 
     # @istest
     def search_2(self):
         # when
         rv = self.app.get('/search?q=one-hash-to-look-for:another-one')
 
         self.assertEquals(rv.status_code, 200)  # check this api
         self.assertRegexpMatches(
             rv.data,
             b'name=q value=one-hash-to-look-for:another-one')
 
     @patch('swh.web.ui.controller.service')
     @istest
     def api_browse(self, mock_service):
         # given
         mock_service.lookup_hash_origin.return_value = {
             'origin': 'some-origin'
         }
 
         # when
         rv = self.app.get('/api/1/browse/sha1:foo/')
 
         self.assertEquals(rv.status_code, 200)
         self.assertEquals(rv.mimetype, 'application/json')
         response_data = json.loads(rv.data.decode('utf-8'))
         self.assertEquals(response_data, {'origin': {'origin': 'some-origin'}})
 
         mock_service.lookup_hash_origin.assert_called_once_with('sha1:foo')
 
     @patch('swh.web.ui.controller.service')
     @istest
     def api_search(self, mock_service):
         # given
         mock_service.lookup_hash.return_value = False
 
         # when
         rv = self.app.get('/api/1/search/sha1:blah/')
 
         self.assertEquals(rv.status_code, 200)
         self.assertEquals(rv.mimetype, 'application/json')
         response_data = json.loads(rv.data.decode('utf-8'))
         self.assertEquals(response_data, {'found': False})
 
         mock_service.lookup_hash.assert_called_once_with('sha1:blah')
 
+    @patch('swh.web.ui.controller.service')
+    @istest
+    def api_1_stat_counters_raise_error(self, mock_service):
+        # given
+        mock_service.stat_counters.side_effect = ValueError(
+            'voluntary error to check the bad request middleware.')
+        # when
+        rv = self.app.get('/api/1/stat/counters')
+        # then
+        self.assertEquals(rv.status_code, 400)
+        self.assertEquals(rv.mimetype, 'application/json')
+        response_data = json.loads(rv.data.decode('utf-8'))
+        self.assertEquals(response_data, {
+            'error': 'voluntary error to check the bad request middleware.'})
+
     @patch('swh.web.ui.controller.service')
     @istest
     def api_1_stat_counters(self, mock_service):
         # given
         mock_service.stat_counters.return_value = {
             "content": 1770830,
             "directory": 211683,
             "directory_entry_dir": 209167,
             "directory_entry_file": 1807094,
             "directory_entry_rev": 0,
             "entity": 0,
             "entity_history": 0,
             "occurrence": 0,
             "occurrence_history": 19600,
             "origin": 1096,
             "person": 0,
             "release": 8584,
             "revision": 7792,
             "revision_history": 0,
             "skipped_content": 0
         }
 
         # when
         rv = self.app.get('/api/1/stat/counters')
 
         response_data = json.loads(rv.data.decode('utf-8'))
         self.assertEquals(rv.status_code, 200)
         self.assertEquals(rv.mimetype, 'application/json')
         self.assertEquals(response_data, {
             "content": 1770830,
             "directory": 211683,
             "directory_entry_dir": 209167,
             "directory_entry_file": 1807094,
             "directory_entry_rev": 0,
             "entity": 0,
             "entity_history": 0,
             "occurrence": 0,
             "occurrence_history": 19600,
             "origin": 1096,
             "person": 0,
             "release": 8584,
             "revision": 7792,
             "revision_history": 0,
             "skipped_content": 0
         })
 
         mock_service.stat_counters.assert_called_once_with()
 
     @patch('swh.web.ui.controller.service')
     @patch('swh.web.ui.controller.request')
     @istest
     def api_uploadnsearch(self, mock_request, mock_service):
         # given
         mock_request.files = {'filename': 'simple-filename'}
         mock_service.upload_and_search.return_value = (
             'simple-filename', 'some-hex-sha1', False)
 
         # when
         rv = self.app.post('/api/1/uploadnsearch/')
 
         self.assertEquals(rv.status_code, 200)
         self.assertEquals(rv.mimetype, 'application/json')
 
         response_data = json.loads(rv.data.decode('utf-8'))
         self.assertEquals(response_data, {'filename': 'simple-filename',
                                           'sha1': 'some-hex-sha1',
                                           'found': False})
 
         mock_service.upload_and_search.assert_called_once_with(
             'simple-filename')