Update stub_component with createStubbedMethods

This is helpful at creating a stub for things like GlModal
which technically has public methods in its API

spec/frontend/__helpers__/stub_component.js

+/**
+ * Returns a new object with keys pointing to stubbed methods
+ *
+ * This is helpful for stubbing components like GlModal where it's supported
+ * in the API to call `.show()` and `.hide()` ([Bootstrap Vue docs][1]).
+ *
+ * [1]: https://bootstrap-vue.org/docs/components/modal#using-show-hide-and-toggle-component-methods
+ *
+ * @param {Object} methods - Object whose keys will be in the returned object.
+ */
+const createStubbedMethods = (methods = {}) => {
+  if (!methods) {
+    return {};
+  }
+
+  return Object.keys(methods).reduce(
+    (acc, key) =>
+      Object.assign(acc, {
+        [key]: () => {},
+      }),
+    {},
+  );
+};
+
 export function stubComponent(Component, options = {}) {
   return {
     props: Component.props,
     model: Component.model,
+    methods: createStubbedMethods(Component.methods),
     // Do not render any slots/scoped slots except default
     // This differs from VTU behavior which renders all slots
     template: '<div><slot></slot></div>',