update App.jsx and improve coverage

abstract LogoutButton to component

src/components/LogoutButton.jsx

@@ -0,0 +1,26 @@
+import React from 'react';
+
+import {
+  Button,
+  ButtonVariant
+} from '@patternfly/react-core';
+
+import { UserIcon } from '@patternfly/react-icons';
+
+const LogoutButton = ({ onDevLogout }) => (
+  <Button
+    id="button-logout"
+    aria-label="Logout"
+    variant={ButtonVariant.plain}
+    onClick={onDevLogout}
+    onKeyDown={event => {
+      if (event.keyCode === 13) {
+        onDevLogout();
+      }
+    }}
+  >
+    <UserIcon />
+  </Button>
+);
+
+export default LogoutButton;