Test updates - still need more coverage

tests/javascripts/support/jest.setup.js

@@ -7,5 +7,11 @@ require('./polyfills.js');
 // Set up jQuery
 global.$ = global.jQuery = require('jquery');
 
+// tests/jest.setup.js
+global.io = jest.fn().mockReturnValue({
+    on: jest.fn(),
+    emit: jest.fn()
+});
+
 // Load module code
 require('govuk_frontend_toolkit/javascripts/govuk/modules.js');