Always set testing cookies, even on pages which do not use them

Addresses #80

Uses code from OpenHumans/open-humans#1109

waffle/middleware.py

@@ -1,11 +1,28 @@
 from django.http import HttpRequest, HttpResponse
 from django.utils.deprecation import MiddlewareMixin
 from django.utils.encoding import smart_str
-
 from waffle.utils import get_setting
+from waffle import get_waffle_flag_model
+
+WaffleFlag = get_waffle_flag_model()
 
 
 class WaffleMiddleware(MiddlewareMixin):
+
+    def __init__(self, get_response):
+        self.get_response = get_response
+
+    def __call__(self, request):
+        """Ensure testing cookie are always set, even if Waffle isn't used"""
+        for flag in WaffleFlag.objects.filter(testing=True):
+            tc = get_setting("TEST_COOKIE") % flag.name
+            if tc in request.GET:
+                on = request.GET[tc] == "1"
+                if not hasattr(request, "waffle_tests"):
+                    request.waffle_tests = {}
+                request.waffle_tests[flag.name] = on
+        return self.process_response(request, self.get_response(request))
+
     def process_response(self, request: HttpRequest, response: HttpResponse) -> HttpResponse:
         secure = get_setting('SECURE')
         max_age = get_setting('MAX_AGE')