[bugfix] Tabs: incorrect line position in some cases (#3961)

test/utils/index.ts

@@ -0,0 +1,17 @@
+import Vue from 'vue';
+import './transition';
+import { mount } from '@vue/test-utils';
+import { trigger, triggerDrag } from './event';
+import { mockScrollTop, mockGetBoundingClientRect } from './dom';
+
+// prevent vue warning log
+Vue.config.silent = true;
+
+// promisify setTimeout
+function later(delay: number = 0): Promise<void> {
+  return new Promise(resolve => {
+    setTimeout(resolve, delay);
+  });
+}
+
+export { mount, later, trigger, triggerDrag, mockScrollTop, mockGetBoundingClientRect };