Remove the client Mock object

It wasn't used by anything so that was easy.  Clean up the test as long as
we're here.

src/allmydata/test/web/common.py

@@ -25,7 +25,8 @@ def assert_soup_has_tag_with_attributes(testcase, soup, tag_name, attrs):
     tags = soup.find_all(tag_name)
     for tag in tags:
         if all(v in tag.attrs.get(k, []) for k, v in attrs.items()):
-            return  # we found every attr in this tag; done
+            # we found every attr in this tag; done
+            return tag
     testcase.fail(
         u"No <{}> tags contain attributes: {}".format(tag_name, attrs)
     )

src/allmydata/test/web/test_root.py

@@ -1,7 +1,13 @@
-from mock import Mock
-
 import time
 
+from urllib import (
+    quote,
+)
+
+from bs4 import (
+    BeautifulSoup,
+)
+
 from twisted.trial import unittest
 from twisted.web.template import Tag
 from twisted.web.test.requesthelper import DummyRequest
@@ -16,6 +22,9 @@ from ...util.connection_status import ConnectionStatus
 from allmydata.web.root import URIHandler
 from allmydata.client import _Client
 
+from .common import (
+    assert_soup_has_tag_with_attributes,
+)
 from ..common_web import (
     render,
 )
@@ -30,28 +39,37 @@ class RenderSlashUri(unittest.TestCase):
     """
 
     def setUp(self):
-        self.client = Mock()
+        self.client = object()
         self.res = URIHandler(self.client)
 
-    def test_valid(self):
+    def test_valid_query_redirect(self):
         """
-        A valid capbility does not result in error
+        A syntactically valid capability given in the ``uri`` query argument
+        results in a redirect.
         """
-        query_args = {b"uri": [
+        cap = (
             b"URI:CHK:nt2xxmrccp7sursd6yh2thhcky:"
             b"mukesarwdjxiyqsjinbfiiro6q7kgmmekocxfjcngh23oxwyxtzq:2:5:5874882"
-        ]}
+        )
+        query_args = {b"uri": [cap]}
         response_body = self.successResultOf(
             render(self.res, query_args),
         )
-        self.assertNotEqual(
-            response_body,
-            "Invalid capability",
+        soup = BeautifulSoup(response_body, 'html5lib')
+        tag = assert_soup_has_tag_with_attributes(
+            self,
+            soup,
+            u"meta",
+            {u"http-equiv": "refresh"},
+        )
+        self.assertIn(
+            quote(cap, safe=""),
+            tag.attrs.get(u"content"),
         )
 
     def test_invalid(self):
         """
-        A (trivially) invalid capbility is an error
+        A syntactically invalid capbility results in an error.
         """
         query_args = {b"uri": [b"not a capability"]}
         response_body = self.successResultOf(