Allow integration tests to access the toolbar

Add a mechanism for integration tests to access the toolbar used for a
particular request:  Update DebugToolbar to emit a signal on creation
referencing itself.  Then create and use a custom Django test client
that connects to this signal to capture the toolbar that was created
while the request was being processed, and to store the toolbar on the
response for use by tests.

Author: living180

debug_toolbar/signals.py

@@ -0,0 +1,4 @@
+from django.dispatch import Signal
+
+# Signal used internally for testing
+toolbar_created = Signal()

debug_toolbar/toolbar.py

@@ -15,6 +15,7 @@
 from django.utils.module_loading import import_string
 
 from debug_toolbar import APP_NAME, settings as dt_settings
+from debug_toolbar.signals import toolbar_created
 
 
 class DebugToolbar:
@@ -38,6 +39,7 @@ def __init__(self, request, get_response):
         self.stats = {}
         self.server_timing_stats = {}
         self.store_id = None
+        toolbar_created.send(request, toolbar=self)
 
     # Manage panels
 

tests/base.py

@@ -1,13 +1,38 @@
 import html5lib
+from asgiref.local import Local
 from django.http import HttpResponse
-from django.test import RequestFactory, TestCase
+from django.test import Client, RequestFactory, TestCase
 
+from debug_toolbar.signals import toolbar_created
 from debug_toolbar.toolbar import DebugToolbar
 
+
+class ToolbarTestClient(Client):
+    def request(self, **request):
+        # Use a thread/async task context-local variable to guard against a
+        # concurrent toolbar_created signal from a different thread/task.
+        data = Local()
+        data.toolbar = None
+
+        def handle_toolbar_created(sender, toolbar=None, **kwargs):
+            data.toolbar = toolbar
+
+        toolbar_created.connect(handle_toolbar_created)
+        try:
+            response = super().request(**request)
+        finally:
+            toolbar_created.disconnect(handle_toolbar_created)
+        response.toolbar = data.toolbar
+
+        return response
+
+
 rf = RequestFactory()
 
 
 class BaseTestCase(TestCase):
+    client_class = ToolbarTestClient
+
     panel_id = None
 
     def setUp(self):