add test coverage for auth utils

src/index.jsx

@@ -78,7 +78,7 @@ export function main (render) {
       <I18n>
         {({ i18n }) => (
           <Background>
-            {!isAuthenticated() ? loginRoutes : (
+            {!isAuthenticated(document.cookie) ? loginRoutes : (
               <Switch>
                 {removeTrailingSlash}
                 <Route path="/login" render={defaultRedirect} />

src/pages/Login.jsx

@@ -110,7 +110,7 @@ class AWXLogin extends Component {
       return null;
     }
 
-    if (isAuthenticated()) {
+    if (isAuthenticated(document.cookie)) {
       return (<Redirect to="/" />);
     }
 

src/util/auth.js

@@ -1,6 +1,6 @@
 // eslint-disable-next-line import/prefer-default-export
-export function isAuthenticated () {
-  const parsed = (`; ${document.cookie}`).split('; userLoggedIn=');
+export function isAuthenticated (cookie) {
+  const parsed = (`; ${cookie}`).split('; userLoggedIn=');
   if (parsed.length === 2) {
     return parsed.pop().split(';').shift() === 'true';
   }