Tests: avoid side effects from build_schema_wrong_backend test

Previously, this would pollute the global settings for the Whoosh
backend causing a failure if the Solr tests ran first. Now this
uses mock.patch which cleans up after itself automatically and
makes the intention of the code immediately obvious

Author: acdha

test_haystack/solr_tests/test_management_commands.py

@@ -1,18 +1,16 @@
 import datetime
-
-from mock import patch
-import pysolr
 from tempfile import mkdtemp
 
+import pysolr
 from django import VERSION as DJANGO_VERSION
 from django.conf import settings
 from django.core.exceptions import ImproperlyConfigured
 from django.core.management import call_command
 from django.test import TestCase
 from django.utils import unittest
+from mock import patch
 
-from haystack import connections
-from haystack import indexes
+from haystack import connections, indexes
 from haystack.utils.loading import UnifiedIndex
 
 from ..core.models import MockModel, MockTag
@@ -145,13 +143,11 @@ def test_multiprocessing(self):
         call_command('update_index', verbosity=2, workers=2, batchsize=5)
         self.assertEqual(self.solr.search('*:*').hits, 23)
 
+    @patch.dict(settings.HAYSTACK_CONNECTIONS['whoosh'], {'PATH': mkdtemp(prefix='dummy-path-')})
     def test_build_schema_wrong_backend(self):
-
-        settings.HAYSTACK_CONNECTIONS['whoosh'] = {'ENGINE': 'haystack.backends.whoosh_backend.WhooshEngine',
-                                                   'PATH': mkdtemp(prefix='dummy-path-'),}
-
         connections['whoosh']._index = self.ui
-        self.assertRaises(ImproperlyConfigured, call_command, 'build_solr_schema',using='whoosh', interactive=False)
+        self.assertRaises(ImproperlyConfigured, call_command, 'build_solr_schema', using='whoosh',
+                          interactive=False)
 
 class AppModelManagementCommandTestCase(TestCase):
     fixtures = ['bulk_data.json']