Add empty authentication module

New versions of vuex warn if there are modules that are used in an
element that haven't had their namespace defined.  This module isn't
actually used in the test, so add an empty Vuex module that matches the
name of AuthenticationStore, so the test can pass.

Change-Id: I5bceb3e1e0bad603028cfb17fa95b020d68ceb4d
Signed-off-by: Ed Tanous <ed@tanous.net>
diff --git a/tests/unit/AppHeader.spec.js b/tests/unit/AppHeader.spec.js
index ed78f03..2d17e76 100644
--- a/tests/unit/AppHeader.spec.js
+++ b/tests/unit/AppHeader.spec.js
@@ -16,7 +16,15 @@
     'global/getSystemInfo': jest.fn(),
   };
 
-  const store = new Vuex.Store({ actions });
+  // VueX requires that all modules be present, even if they aren't used
+  // in the test, so invent a Fake auth module and install it.
+  const modules = {
+    authentication: {
+      namespaced: true,
+    },
+  };
+
+  const store = new Vuex.Store({ actions, modules });
   const wrapper = mount(AppHeader, {
     store,
     localVue,