Set function scope for logged-out webtest fixture

I mistakenly assumed that not setting the cookiejar argument when
creating a webtest TestApp would mean that no cookies would be retained
between requests, but that's wrong. If you don't pass a cookiejar, it
just automatically creates one for you. Because of this, logged-out
webtests would end up being logged-in after any test logged in.

This reduces the webtest_loggedout fixture's scope to function-level so
that it will be re-initiated on every test instead. It also stops
passing a cookiejar for the logged-in webtest, since that's unnecessary.

tildes/tests/conftest.py

@@ -2,7 +2,6 @@
 # SPDX-License-Identifier: AGPL-3.0-or-later
 
 import os
-from http.cookiejar import CookieJar
 
 from pyramid import testing
 from pyramid.paster import get_app, get_appsettings
@@ -210,7 +209,7 @@ def base_app(overall_redis_session, sdb):
 @fixture(scope="session")
 def webtest(base_app):
     """Create a webtest TestApp and log in as the SessionUser account in it."""
-    app = TestApp(base_app, extra_environ=WEBTEST_EXTRA_ENVIRON, cookiejar=CookieJar())
+    app = TestApp(base_app, extra_environ=WEBTEST_EXTRA_ENVIRON)
 
     # fetch the login page, fill in the form, and submit it (sets the cookie)
     login_page = app.get("/login")
@@ -221,7 +220,7 @@ def webtest(base_app):
     yield app
 
 
-@fixture(scope="session")
+@fixture(scope="function")
 def webtest_loggedout(base_app):
-    """Create a logged-out webtest TestApp (no cookies retained)."""
+    """Create a logged-out webtest TestApp (function scope, so no state is retained)."""
     yield TestApp(base_app, extra_environ=WEBTEST_EXTRA_ENVIRON)