Copy vue_mount_component_helper.js to Jest

spec/frontend/helpers/vue_mount_component_helper.js

+import Vue from 'vue';
+
+const mountComponent = (Component, props = {}, el = null) =>
+  new Component({
+    propsData: props,
+  }).$mount(el);
+
+export const createComponentWithStore = (Component, store, propsData = {}) =>
+  new Component({
+    store,
+    propsData,
+  });
+
+export const mountComponentWithStore = (Component, { el, props, store }) =>
+  new Component({
+    store,
+    propsData: props || {},
+  }).$mount(el);
+
+export const mountComponentWithSlots = (Component, { props, slots }) => {
+  const component = new Component({
+    propsData: props || {},
+  });
+
+  component.$slots = slots;
+
+  return component.$mount();
+};
+
+/**
+ * Mount a component with the given render method.
+ *
+ * This helps with inserting slots that need to be compiled.
+ */
+export const mountComponentWithRender = (render, el = null) =>
+  mountComponent(Vue.extend({ render }), {}, el);
+
+export default mountComponent;