Django 1.10: Use single cache prefix for casper tests.

There is a change in Django 1.10 due to which whenever the password
of the user is changed the session hash changes. This change affects
us because we cache user profile objects and these cached objects need
to be refreshed. However, the signal sent by Django in which objects are
refreshed fails to refresh the cache for Tornado because it uses a
different cache prefix.

Note: Backend tests are not affected because they don't rely on Tornado.

frontend_tests/run-casper

@@ -27,6 +27,7 @@ except ImportError as e:
 #
 
 os.environ["TORNADO_SERVER"] = "http://127.0.0.1:9983"
+os.environ["CASPER_TESTS"] = "1"
 os.environ["PHANTOMJS_EXECUTABLE"] = os.path.join(os.path.dirname(__file__), "../node_modules/.bin/phantomjs")
 
 usage = """%prog [options]

zerver/lib/cache.py

@@ -61,18 +61,18 @@ def remote_cache_stats_finish():
 
 def get_or_create_key_prefix():
     # type: () -> text_type
-    if settings.TEST_SUITE:
+    if settings.CASPER_TESTS:
         # This sets the prefix for the benefit of the Casper tests.
-        # The Python tests overwrite KEY_PREFIX on each test, but use
-        # this codepath as well, just to save running the more complex
-        # code below for reading the normal key prefix.
         #
         # Having a fixed key is OK since we don't support running
         # multiple copies of the casper tests at the same time anyway.
-        if settings.TORNADO_SERVER:
-            return u'casper_tests:'
-        else:
-            return u'django_tests:'
+        return u'casper_tests:'
+    elif settings.TEST_SUITE:
+        # The Python tests overwrite KEY_PREFIX on each test, but use
+        # this codepath as well, just to save running the more complex
+        # code below for reading the normal key prefix.
+        return u'django_tests_unused:'
+
     # directory `var` should exist in production
     subprocess.check_call(["mkdir", "-p", os.path.join(settings.DEPLOY_ROOT, "var")])
 

zproject/settings.py

@@ -78,6 +78,8 @@ else:
 TEST_SUITE = False
 # The new user tutorial is enabled by default, but disabled for client tests.
 TUTORIAL_ENABLED = True
+# This is overridden in test_settings.py for the test suites
+CASPER_TESTS = False
 
 # Import variables like secrets from the prod_settings file
 # Import prod_settings after determining the deployment/machine type

zproject/test_settings.py

@@ -51,6 +51,9 @@ else:
     CAMO_URI = 'https://external-content.zulipcdn.net/'
     CAMO_KEY = 'dummy'
 
+if "CASPER_TESTS" in os.environ:
+    CASPER_TESTS = True
+
 # Decrease the get_updates timeout to 1 second.
 # This allows CasperJS to proceed quickly to the next test step.
 POLL_TIMEOUT = 1000