Harden the queries_captured() test decorator.

Before, it was trying to use connection.queries, but Django
could pull the rug out from under us.  Now we monkeypatch
the CursorDebugWrapper methods instead.

(imported from commit 25d5bab47673f2b66a6325f48d33e66c31055ab3)

zerver/tests.py

@@ -6,6 +6,7 @@ from django.test.simple import DjangoTestSuiteRunner
 from django.utils.timezone import now
 from django.core.exceptions import ValidationError
 from django.db.models import Q
+from django.db.backends.util import CursorDebugWrapper
 
 from zerver.models import Message, UserProfile, Stream, Recipient, Subscription, \
     get_display_recipient, Realm, Client, \
@@ -57,11 +58,41 @@ def queries_captured():
     Allow a user to capture just the queries executed during
     the with statement.
     '''
+
+    queries = []
+
+    def wrapper_execute(self, action, sql, params=()):
+        self.set_dirty()
+        start = time.time()
+        try:
+            return action(sql, params)
+        finally:
+            stop = time.time()
+            duration = stop - start
+            queries.append({
+                    'sql': sql,
+                    'time': "%.3f" % duration,
+                    })
+
     old_settings = settings.DEBUG
     settings.DEBUG = True
-    connection.queries = []
+
-    yield connection.queries
+    old_execute = CursorDebugWrapper.execute
+    old_executemany = CursorDebugWrapper.executemany
+
+    def cursor_execute(self, sql, params=()):
+        return wrapper_execute(self, self.cursor.execute, sql, params)
+    CursorDebugWrapper.execute = cursor_execute
+
+    def cursor_executemany(self, sql, params=()):
+        return wrapper_execute(self, self.cursor.executemany, sql, params)
+    CursorDebugWrapper.executemany = cursor_executemany
+
+    yield queries
+
     settings.DEBUG = old_settings
+    CursorDebugWrapper.execute = old_execute
+    CursorDebugWrapper.executemany = old_executemany
 
 
 def bail(msg):