Add tests for survey_banner.vue

spec/frontend/serverless/survey_banner_spec.js

+import { mount } from '@vue/test-utils';
+import Cookies from 'js-cookie';
+import SurveyBanner from '~/serverless/survey_banner.vue';
+import { GlBanner } from '@gitlab/ui';
+
+describe('Knative survey banner', () => {
+  let wrapper;
+
+  function mountBanner() {
+    wrapper = mount(SurveyBanner, {
+      propsData: {
+        surveyUrl: 'http://somesurvey.com/',
+      },
+    });
+  }
+
+  afterEach(() => {
+    if (wrapper) wrapper.destroy();
+  });
+
+  it('should render the banner when the cookie is absent', () => {
+    jest.spyOn(Cookies, 'get').mockReturnValue(undefined);
+    mountBanner();
+
+    expect(Cookies.get).toHaveBeenCalled();
+    expect(wrapper.find(GlBanner).exists()).toBe(true);
+  });
+
+  it('should close the banner and set a cookie when close button is clicked', () => {
+    jest.spyOn(Cookies, 'get').mockReturnValue(undefined);
+    jest.spyOn(Cookies, 'set');
+    mountBanner();
+
+    expect(wrapper.find(GlBanner).exists()).toBe(true);
+    wrapper.find(GlBanner).vm.$emit('close');
+
+    return wrapper.vm.$nextTick().then(() => {
+      expect(Cookies.set).toHaveBeenCalledWith('hide_serverless_survey', 'true', { expires: 3650 });
+      expect(wrapper.find(GlBanner).exists()).toBe(false);
+    });
+  });
+
+  it('should not render the banner when the cookie is set', () => {
+    jest.spyOn(Cookies, 'get').mockReturnValue('true');
+    mountBanner();
+
+    expect(Cookies.get).toHaveBeenCalled();
+    expect(wrapper.find(GlBanner).exists()).toBe(false);
+  });
+});