Throw error for multiple RecaptchaModal instances

app/assets/javascripts/vue_shared/components/recaptcha_modal.vue

@@ -30,9 +30,16 @@ export default {
   },
 
   mounted() {
+    if (window.recaptchaDialogCallback) {
+      throw new Error('recaptchaDialogCallback is already defined!');
+    }
     window.recaptchaDialogCallback = this.submit.bind(this);
   },
 
+  beforeDestroy() {
+    window.recaptchaDialogCallback = null;
+  },
+
   methods: {
     appendRecaptchaScript() {
       this.removeRecaptchaScript();

spec/javascripts/issue_show/components/description_spec.js

 import $ from 'jquery';
 import Vue from 'vue';
+import '~/behaviors/markdown/render_gfm';
 import Description from '~/issue_show/components/description.vue';
 import mountComponent from 'spec/helpers/vue_mount_component_helper';
 
@@ -91,6 +92,7 @@ describe('Description component', () => {
     let TaskList;
 
     beforeEach(() => {
+      vm.$destroy();
       vm = mountComponent(
         DescriptionComponent,
         Object.assign({}, props, {